I-NRLF 


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K  E  L  E  Y 

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L 

UNIVERSITY   OF 
V       CALIFORNIA 

EARTH 

SCIENCES 

LIBRARY 


MINERALS  AND  ROCKS 


MINERALS  AND    ROCKS 


THE   ELEMENTS  OF  MINERALOGY  AND   LITHOLOGY 
FOR  THE  USE  OF 

STUDENTS  IN  GENERAL  GEOLOGY 


BY 

WILLIAM  SHIRLEY  BAYLEY,  PH.D. 

PROFESSOR  OF  GEOLOGY  IN  THE  UNIVERSITY  OF  ILLINOIS 


NEW  YORK  AND  LONDON 
D.  APPLETON  AND  COMPANY 

1921 


EARTH 

SCIENCES 

LIBRARY 


I 
COPYRIGHT,  1915,  BT 

D.  APPLETON  AND  COMPANY 


Printed  in  the  United  States  of  America 


35 


2- 

EARTH 

PBEFACB 


THIS  brief  description  of  the  most  important  minerals 
and  rocks  is  intended  for  the  use  of  students  in  geology 
who  wish  some  familiarity  with  the  material  of  the  earth's 
crust,  but  who  may  not  find  the  time  for  courses  in  mineral- 
ogy and  lithology.  It  was  written  in  the  hope  that  it  might 
serve  a  useful  purpose  as  a  laboratory  guide.  The  min- 
erals and  rocks  chosen  for  description  are  those  which  are 
most  frequently  met  with  and,  in  addition,  those  which, 
though  uncommon,  are  for  some  reason  of  special  interest. 

Only  so  much  of  the  description  of  each  mineral  is  given 
as  is  essential  to  its  recognition.  All  unessential  details 
are  omitted.  For  occurrence  and  crystallization  more  com- 
plete treatises  must  be  consulted. 

On  the  other  hand,  the  blowpipe  tests  are  given  fully  in 
order  that  the  student  in  the  field  may  be  able  to  recognize 
the  chemical  constituents  of  minerals  with  which  he  may 
not  be  familiar. 

The  discussion  of  rocks  is  intended  to  be  mainly  sugges- 
tive. It  is  believed  that  it  is  of  much  more  value  to  the 
student  to  understand  the  significance  of  his  rock  specimens 
than  to  be  able  to  identify  them  by  name.  Only  the  com- 
monest rock  names  are  defined.  The  rock  groups  are  em- 
phasized. 

The  * '  Keys ' '  for  the  determination  of  minerals  and  rocks 
are  merely  guides  to  the  descriptions  in  the  body  of  the  text. 

The  author  wishes  to  acknowledge  his  indebtedness  to 
Dana's  Text  Book  of  Mineralogy  and  Moses  and  Parson's 
Mineralogy  for  many  of  the  crystal  illustrations  which  ap- 
pear in  this  volume.  His  thanks  are  due  to  Mr.  C.  S.  Ross., 

470638 


PREFACE 

assistant  in  geology  at  the  University  of  Illinois,  for  most 
of  the  photographs  from  which  the  half-tones  were  made. 

The  author  is  under  obligations  to  the  McGraw-Hill 
Book  Company  for  the  loan  of  the  cuts  from  which  figures 
1,  2,  29,  33,  34,  37,  51,  77,  78,  89  and  94  were  printed. 
These  illustrations  originally  appeared  in  the  author's 
Elementary  Crystallography,  issued  in  1910. 

WILLIAM  SHIRLEY  BAYLEY. 


CONTENTS 

I.    MINERALS      <• 

PAGE 

I.  INTRODUCTION 1 

II.  DESCRIPTION  OF  MINERALS 7 

Elements 7 

Sulphides :       ....  12 

Arsenides  and  Sulph-Arsenides 22 

Sulph-Arsenites  and  Sulph-Antimonites      ...  25 

Chlorides  and  Fluorides 27 

Nitrates 31 

Borates 31 

Oxides 33 

Hydroxides 42 

Aluminates,  Ferrites  and  Chromites     ....  46 

Carbonates 49 

Normal  Carbonates 49 

Basic  Carbonates 59 

Sulphates ..60 

Anhydrous  Sulphates 60 

Hydrated  Sulphates 64 

Tungstates,  Molybdates  and  Chromates     ...  66 

Phosphates,  Arsenates  and  Vanadates         ...  70 

Apatite  Group 70 

Hydrated  Phosphates  and  Arsenates           .       .  74 
Columbates  and  Tantalates  .       .       .       .       .       .77 

Uranyl  Compounds .80 

Silicates 82 

Anhydrous  Silicates 83 

Pyroxenes  and  Amphiboles    ....  106 

Feldspars 112 

Hydrated  Silicates .119 

Zeolites 121 

Titanates  and  Titano-Silicates 125 

vii 


viii  CONTENTS 

PAGE 

III.  DETERMINATION  OF  MINERALS  WITH  THE  AID  OF  THE 

BLOWPIPE 128 

IV.  CHARACTERISTIC  REACTIONS  OF  THE  MORE  IMPORTANT 

ELEMENTS  AND  ACID  RADICALS  .....  151 

V.  KEY  TO  THE  DETERMINATION  OF  MINERALS  .       .       .  168 
VI.  LIST  OF  MINERALS  ARRANGED  ACCORDING  TO  THEIR 

IMPORTANT  CONSTITUENTS 181 

ii.  ROCKS] 

I.  SYNOPSIS  OF  A  CLASSIFICATION  OF  ROCKS      .       .       .  189 
Crystalline  Rocks     .       .       .       .       *       .       .       .190 

Fragmental  Rocks 200 

Other  Rocks 206 

II.  KEY  TO  THE  DETERMINATION  OF  ROCKS  (EXCEPT  COAL)  .  207 

INDEX  219 


I 

MINERALS 


MINERALS    AND    ROCKS 


INTRODUCTION 

THE  solid  portion  of  the  earth's  surface  consists  of 
rocks  which  are  composed  either  of  minerals  (granite), 
or  of  the  hard  parts  of  animals  (shell  limestone)  or 
plants,  or  of  their  decomposition  products  (coal), 
or  of  mixtures  of  organic  and  inorganic  matter 
(many  limestones).  The  rocks  form  the  earth's  crust 
in  the  same  way  that  floors,  walls,  etc.,  form  a  build- 
ing. They  are  architectural  units.  The  materials 
constituting  the  rocks  may  be  likened  to  the  bricks  of 
the  walls  or  to  the  boards  of  the  floors.  Most  rocks 
are  composed  of  minerals  or  of  mixtures  of  mineral 
and  organic  matter.  Moreover,  much  of  the  matter 
of  organic  origin  has  the  same  composition  as  some  of 
the  mineral  matter;  consequently,  a  knowledge  of 
minerals  is  essential  before  the  character  of  the  rocks 
can  be  properly  appreciated.  Further,  many  of  the 
minerals  occurring  in  the  earth's  crust  are  of  great 
economic  importance,  because  from  them  we  obtain 
the  metals,  and  make  sulphuric  acid,  glass  and  many 
other  substances  that  enter  so  largely  into  the  life  of 
civilized  beings.  Although  some  1,200  different  min- 
eral substances  have  been  assigned  names,  only  a 


2,V;/^  .  -f:  ;\ .MINERALS  AND  ROCKS 

comparatively  few  of  these  are  important,  either  as 
constituents  of  rocks,  or  as  sources  of  materials  useful 
to  man. 

Minerals. — A  mineral  is  an  inorganic,  natural 
compound  that  occurs  in  the  earth's  crust.  Most 
minerals  are  definite  chemical  compounds,  but  some 
are  mixtures  of  several  compounds  and  others  are  solid 
solutions  of  several  substances  in  one  another. 
Whether  a  definite  compound  or  a  mixture,  every 
mineral  is  characterized  by  individual  properties 
and  usually  by  distinct  forms  (crystals),  and  by  these 
properties  we  recognize  them. 

Chemically,  minerals  are  elements,  sulphides,  ox- 
ides, hydroxides  or  the  salts  of  various  acids.  Most 
of  the  common  ones  are  anhydrous,  but  a  few,  appar- 
ently, consist  of  salts  combined  with  water,  thus: 
gypsum  =  CaSO4  +2H20. 

Determination  of  Minerals. — Some  minerals  are 
so  plainly  characterized  that  they  may  be  recognized 
at  a  glance.  Many  others  may  be  determined  by  the 
application  of  a  few  simple  physical  tests.  A  few 
require  the  application  of  chemical  tests  before  their 
true  nature  may  be  appreciated.  The  chemical  tests 
that  can  be  applied  most  conveniently  are  those  based 
on  reactions  with  dry  reagents  at  high  temperatures. 
Because  high  temperatures  are  most  readily  obtained 
by  the  aid  of  a  blowpipe,  reactions  of  this  kind  are 
known  as  blowpipe  reactions,  and  the  tests  applied 
are  designated  blowpipe  tests. 

Physical  Properties. — The  physical  properties  of 
most  value  in  diagnosis  are:  Form,  color,  streak, 
luster,  hardness,  tenacity,  and  specific  gravity  or 
density. 


INTRODUCTION        .  •  *J     : .  S  '*  V ; fl 

Form. — Substances  passing  from  the  fluid  to  the 
solid  state  usually  assume  certain  definite  forms  that 
are  characteristic.  These  substances,  if  not  prevented 
from  doing  so  by  external  conditions,  bound  them- 
selves by  plane  surfaces  according  to  certain  definite 
arrangements.  A  body  so  bounded  is  a  crystal,  and 
the  process  of  forming  crystals  is  crystallization. 

Crystals  are  divisible  into  six  groups,  or  systems, 
known  as  isometric,  hexagonal,  tetragonal,  ortho- 
rhombic,  monoclinic  and  triclinic,  in  accordance  with 
the  symmetry  exhibited  by  the  arrangement  of  their 
faces.  The  systematic  study  of  such  forms  is  known 
as  crystallography.  In  many  cases  the  manner  of 
crystallization  of  a  mineral  is  so  characteristic  that  the 
forms  of  its  crystals  serve  to  distinguish  it. 

Color  or  Streak. — The  color  exhibited  by  a  mineral 
in  reflected  light  may  be  inherent  to  its  substance 
(is  ideochromatic)  or  it  may  be  due  to  impurities 
included  in  its  substance  (is  allochromatic) .  Thus, 
common  salt  is  white  or  colorless,  but  many  speci- 
mens are  gray  because  contaminated  with  a  little 
dark  clay.  When  in  powdered  form,  the  mineral 
more  nearly  exhibits  its  true  color  than  when  in  larger 
masses,  because  the  quantity  of  impurity  in  a  grain 
of  powder  is  too  small  to  affect  its  color  materially. 
The  most  convenient  method  of  viewing  the  powder 
of  a  mineral  is  by  examining  the  mark,  or  streak,  made 
by  drawing  it  across  a  piece  of  rough  porcelain  or  other 
hard,  white  substance.  The  color  of  a  mineral's 
streak  is,  therefore,  more  characteristic  than  that  of 
its  large  fragments. 

Luster. — The  amount  and  character  of  the  light 
reflected  from  a  surface  is  known  as  its  luster.  If  a 


IP  V;  MINERALS  AND  ROCKS 

substance  is  opaque  and  none  of  the  light  that  falls 
upon  it  penetrates  its  surface,  its  luster  is  like  that  of 
metals,  is  metallic.  If  a  portion  of  the  incident  light 
is  diffracted  and  the  surface  exhibits  a  play  of  colors 
as  does  a  pearl,  or  the  inside  of  a  mussel  shell,  its  luster 
is  pearly.  Other  lusters  are  glassy  or  vitreous, 
greasy,  silky,  etc. 

Hardness. — The  hardness  of  a  substance  may  be 
tested  by  comparing  it  with  a  standard  series  of  sub- 
stances of  different  grades  of  hardness.  Among 
mineralogists  the  standard  scale  of  hardness,  known  as 
Moh's  scale,  consists  of  ten  minerals  arranged  accord- 
ing to  their  increasing  hardness  as  follows : 

Moh's  Scale  of  Hardness 

1.  Talc  6.  Feldspar 

2.  Gypsum  7.  Quartz 

3.  Calcite  8.  Topaz 

4.  Fluorite  9.  Corundum 

5.  Apatite  10.  Diamond 

A  mineral  that  will  not  scratch  any  given  mineral 
in  the  scale  of  hardness  nor  be  scratched  by  it  possesses 
an  equal  hardness.  If  it  scratches  one  of  the  scale 
minerals  and  is  scratched  by  the  next  hardest  one, 
its  position  with  respect  to  hardness  is  between  the 
two.  Thus,  a  mineral. that  scratches  feldspar  but  is 
scratched  by  quartz  has  a  hardness  between  6  and  7. 

A  mineral  that  can  be  scratched  by  the  thumb-nail 
has  a  hardness  of  2  or  less;  if  it  can  be  scratched  by  a 
copper  coin,  its  hardness  is  not  greater  than  about 
3.5;  if  by  glass,  its  hardness  is  less  than  5.5,  and  if 
by  the  blade  of  a  pocketknife,  its  hardness  is  less  than 
6.5.  Any  mineral  that  will  scratch  quartz  has  a  hard- 
ness exceeding  7. 


INTRODUCTION  5 

Tenacity. — With  respect  to  tenacity,  substances 
may  be  distinguished  as  brittle,  sectile,  malleable, 
flexible  and  elastic.  A  brittle  substance  flies  into 
powder  when  cut  with  a  knife.  A  sectile  substance 
may  be  cut,  but  it  pulverizes  under 
blows.  A  malleable  substance  flat- 
tens when  hammered.  A  flexible 
substance  will  bend  and  remain 
bent  when  the  action  of  the  deform- 
ing force  ceases.  An  elastic  body 
will  bend,  but  will  recover  its 
original  position  when  the  bending 
force  is  no  longer  active.  Glass 
is  brittle;  copper,  malleable;  gyp- 
sum, sectile;  asbestos,  flexible; 
and  mica,  elastic. 

Density. — The  density  of  a 
substance  compared  with  that  of 
water  is  its  specific  gravity.  Rock 
salt  has  a  sp.gr.  of  2.1;  quartz  of 
about  2.7;  garnet  of  3.75;  magnet- 
ite of  5.2  and  iron  of  7.3.  Since 
a  cubic  foot  of  water  weighs  about 
62 J  Ibs.,  the  weight  of  a  cubic 
foot  of  any  other  substance  can  be 
calculated  by  multiplying  its  sp.gr. 
by  62|  Ibs.  In  the  case  of  minerals 
of  similar  appearance  their  specific 
gravities  are  often  of  diagnostic  im- 
portance. Thus,  barite  (BaS04)  has  a  sp.gr.  of  about  4.4, 
while  for  anhydrite  (CaSO4)  the  sp.gr.  is  only  about  3.3. 
The  most  convenient  method  for  determining  the  sp.gr. 
of  minerals  is  by  means  of  the  Jolly  balance  (Fig.  1). 


6  MINERALS  AND  ROCKS 

Cleavage. — Many  substances  that  crystallize  pos- 
sess a  marked  tendency  to  split  along  certain  directions 
in  preference  to  others,  in  consequence  of  differences 
in  cohesive  power  in  different  directions.  This  prop- 


FIG.  2. — Cleavage  Cracks  in  Calcite. 

erty  is  known  as  cleavage.  It  is  very  characteristic 
of  certain  substances  and  may  be  used  to  distinguish 
them.  For  instance,  calcite  (CaCOs)  cleaves  in  such 
a  way  as  to  yield  fragments  that  are  rhombohedrons 
(figures  bounded  by  six  similar  rhombs).  (See  Fig.  2.) 


II 

DESCRIPTION  OF  MINERALS 
ELEMENTS 

AMONG  the  elements  that  occur  native  are  two 
important  non-metals  and  three  metals.  All  are  of 
economic  importance. 

1.  Diamond  (C)  is  found  in  crystals,  crystal 
fragments,  crystalline  masses  and  rounded  pebbles. 


FIG.  3. — Crystal  of  Diamond  FIG.  4. — Photograph  of  Dia- 

with  Curved  Faces.  mond  Crystal. 

Its  crystals  are  octahedral  in  general  habit,  with 
their  edges  rounded,  and  frequently  with  curved 
faces  (Fig.  3  and  Fig.  4).  They  possess  an  easy  cleave- 
age  parallel  to  octahedral  planes. 

The  mineral  is  colorless,  blue,  yellow,  gray  or  black, 
and  transparent  or  translucent.  Its  streak  is  color- 
less, and  its  luster  adamantine,  i.e.,  like  that  of  greasy 
glass.  Its  hardness  is  10  and  its  sp.gr.  3.15  to  3.5. 
One  of  its  most  characteristic  features  is  its  high  index 
of  refraction  (2.4195  for  yellow  light)  which  causes 
transparent  stones  to  exhibit  a  marked  brilliancy. 


8  MINERALS  AND  ROCKS 

Three  varieties  are  recognized: 

Diamond,  transparent,  light-colored. 
Carbonado,  or  black  diamond,  dark-colored  and 
opaque    without    distinct    cleavage.      Sp.gr. 
3.15-3.3. 

Bort,  dark-colored  crystalline  aggregates.    Sp.gr. 
3.5. 

Before  the  blowpipe,   diamond  powder  is  slowly 
consumed.     The  mineral  is  insoluble  in  acids. 
'      Diamond   is   easily   distinguished   from  all   other 
minerals  by  its  extreme  hardness. 

The  mineral  occurs  as  crystals  in  a  basic  igneous 
rock  cutting  through  a  carbonaceous  shale;  as  crystals 
and  rounded  pebbles  in  sandstones  and  conglomerates, 
and  as  pebbles  in  river  sands. 

The  dark  varieties  of  diamonds  are  used  in  cutting 
and  grinding  instruments.  Their  powder  is  used  for 
polishing.  Transparent  varieties  are  cut  and  employed 
as  gems. 

2.  Graphite  is  another  form  of  carbon.  It  is  a 
grayish-black  substance  that  usually  occurs  in  scales 
or  in  dull  black,  earthy  masses  or  in  small  grains. 
When  pure,  it  has  a  metallic' luster,  a  black  streak 
and  is  so  soft  that  it  leaves  a  mark  on  paper.  It  is 
easily  cleavable  into  thin  plates  that  are  flexible. 
Sp.gr.  is  about  2.25. 

It  is  infusible  and  non-combustible  at  the  temper- 
atures produced  by  the  blowpipe;  and  it  is  unattacked 
by  acids.  It  is  distinguished  from  all  other  minerals 
but  molybdenite  (No.  8)  by  its  color,  softness  and 
infusibility.  It  is  distinguished  from  molybdenite  by 
the  absence  of  sulphur. 

Graphite  occurs  as  scales  and  plates  in  limestones, 


DESCRIPTION  OF  MINERALS  9 

shales,  clays,  gneisses,  granites  and  other  rocks,  and 
in  veins. 

Crude  graphite,  plumbago,  or  black  lead,  is  used 
in  the  manufacture  of  stove  polishes  and  paint.  Pure 
varieties  are  compressed  into  "  centers "  for  lead 
pencils,  and  ground  for  use  in  lubricators. 

3.  Sulphur  occurs  in  nature  as  a  powder,  as  globular 
masses,  as  stalactites  and  in  crystals  (Fig.  5).     When 
pure,  it  has  a  lemon-yellow  color  and  streak,  a  glassy 
or   resinous  luster,   a  hardness   of   1.5-2,   and  sp.gr. 
about  2.     It  is  transparent   or  trans- 
lucent, and  brittle.     It  is  insoluble  in 

water  or  acids,  but  is  soluble  in  carbon- 
bisulphide,  chloroform  and  turpentine. 
At  113°  it  melts.     It  ignites  at  270°    pIG>  5^— sulphur 
and    burns    with    a    blue    flame,   pro-         Crystal, 
ducing  at  the  same  time  the  choking  fumes  of  SO 2. 

Massive  sulphur  varies  in  color  from  yellow  to 
brown,  gray,  etc.,  according  to  the  impurities  in  it. 

Sulphur  is  found  principally  in  the  vicinity  of 
volcanoes  and  certain  hot  springs  as  pow^der,  or  as 
little  crystals  implanted  on  the  walls  of  cracks  in  rocks, 
or  as  crystalline  particles  in  the  cavities  of  porous 
limestones  associated  with  gypsum  (No.  67). 

There  are  only  a  very  few  minerals  that  are  apt 
to  be  confused  with  sulphur.  Sulphur  may  be  dis- 
tinguished from  all  of  them  by  its  softness,  brittleness 
and  its  low  melting-point. 

The  mineral  is  used  principally  in  the  manufacture 
of  sulphuric  acid,  of  insecticides,  gunpowder,  etc. 

4.  Copper,  in  its  native  condition,  is  similar  to  the 
metal  in  common  use  except  that  its  surface  is  usually 
tarnished  by  a  black  coating,  which  must  be  removed 


10  MINERALS  AND  BOCKS 

before  the  characteristic  color  of  the  metal  can  be  seen. 
Its  hardness  is  2.5-3  and  its  sp.gr.  8.9. 

Copper  melts  at  a  comparatively  low  temperature. 
Upon  cooling,  the  fused  mass  becomes  covered  with 
a  coating  of  black  oxide.  Copper  dissolves  in  nitric 
acid  with  the  evolution  of  brownish-red  fumes  of 
nitrous  oxide  and  the  production  of  a  blue  solution, 
which,  upon  the  addition  of  an  excess  of  ammonia, 
turns  to  a  brilliant  purple -blue.  A  piece  of  bright 
iron  placed  in  the  acid  solution  becomes  .covered  with 
a  coating  of  metallic  copper.  When  heated  in  the 
flame  of  the  blowpipe,  copper  imparts  to  it  a  green 
color  which  changes  to  azure-blue  when  the  metal  is 
touched  with  a  drop  of  HC1. 

Copper  is  easily  distinguished  from  all  other  miner- 
als but  gold  by  its  color  and  malleability.  It  is  dis- 
tinguished from  gold  by  its  solubility  in  nitric  acid. 

The  native  metal  is  utilized  as  a  source  of  the 
commercial  metal.  Most  of  the  metal  used  in  the 
arts,  however,  is  obtained  from  its  compounds  (see 
chalcopyrite,  No.  17)  and  bornite  (No.  18). 

Copper  occurs  as  grains  and  crystals  in  cavities 
in  volcanic  and  sedimentary  lavas,  as  scales  between 
the  layers  of  sedimentary  rocks  and  as  crystals  with 
calcite  (No.  50)  in  veins. 

5.  Silver,  in  its  native  state,  is  identical  in  its 
properties  with  the  commercial  metal.  It  is,  however, 
usually  tarnished  by  a  black  or  gray  stain.  Silver 
is  malleable.  Its  hardness  is  2.5-3,  and  its  sp.gr. 
10.92. 

The  metal  dissolves  readily  in  dilute  HNOs,  yield- 
ing a  colorless  solution  from  which  a  silver  coating 
is  deposited  on  a  strip  of  bright  copper  placed  within 


DESCRIPTION  OF  MINERALS  11 

it.  Fragments  fuse  easily  to  silver-white  pellets  that 
are  distinguished  from  lead  and  tin  by  the  reaction 
just  described  and  by  the  fact  that  they  dissolve  in 
HNOs  and  form  a  solution  from  which  hydrochloric 
acid  throws  down  a  white  precipitate  (AgCl),  which 
is  insoluble  in  hot  water.  It  is  distinguished  from 
galena  (No.  9)  and  mica  (Nos.  95-99),  which  it  some- 
times resembles  in  appearance,  by  its  malleability  and 
its  silver-white  color. 

Silver  occurs  in  veins,  with  or  without  other  min- 
erals, as  small  particles  scattered  through  various 
rocks,  mixed  with  oxidation  products  of  a  wide  range 
of  minerals  in  the  upper  portions  of  veins  containing 
silver  ores,  and  as  pellets  in  the  sands  of  streams 
(placer  deposits). 

6.  Gold. — Native  gold  is  the  principal  source  of  the 
metal  used  in  the  arts.  It  is  similar  in  all  respects 
to  the  commercial  metal.  Its  hardness  is  2.5-3  and 
sp.gr.  19.5.  Its  color  varies  with  the  impurities 
occurring  with  it.  Silver  makes  its  color  paler  and 
copper  imparts  to  it  a  reddish  tinge.  Gold  is  so 
malleable  that  it  can  be  hammered  into  sheets  that 
are  so  thin  as  to  be  translucent  with  a  blue  or  green 
color. 

The  mineral  fuses  easily  in  the  blowpipe  flame. 
It  is  insoluble  in  any  single  acid,  but  is  dissolved  in 
aqua-regia  (2  pts.  HC1  and  1  pt.  HNOs). 

Gold  is  distinguished  from  copper  (No.  4)  by  its 
insolubility  in  HNOs;  from  pyrite  (No.  14)  and  chal- 
copyrite  (No.  17)  by  its  malleability,  and  from  yellow 
mica  by  its  insolubility  and  malleability. 

It  occurs  as  grains  and  pellets  in  placer  deposits 
and  associated  with  quartz  and  pyrite  (Nos.  34  and 


12  MINERALS  AND  ROCKS 

14)  in  veins.     It  is  found  also  disseminated  in  tiny 
grains  in  slates  and  quartzites. 

SULPHIDES 

The  sulphides  are  compounds  derived  from  H2S 
by  the  replacement  of  the  H  by  metals.  All  sul- 
phides when  roasted  yield  S02  and,  when  fused  on 
charcoal  with  Na2C03,  they  form  Na2S,  which  is 
soluble  in  water.  The  solution  placed  on  a  clean  piece 
of  silver  will  produce  a  brown  or  black  stain.  Most 
of  the  sulphides  are  mined  as  ores  of  the  metals. 

7.  Stibnite  (Sb2S3)  is  the  principal  ore  of  anti- 
mony. It  occurs  in  acicular  and  prismatic  crystals 
(Fig.  6),  in  radiating  groups  of  crystals 
and  in  fibrous  masses.  Many  of  the 
crystals  are  curved  or  bent  and  nearly 
all  are  vertically  striated. 

Stibnite  is  dark  gray  and  its  streak 
FIG.  6—  Stibnite  a  little  darker.  Exposed  surfaces  are 
often  coated  with  a  black  or  irides- 
cent tarnish.  Its  luster  is  metallic  in  masses;  but 
thin  splinters  are  translucent  in  reddish  tints.  It 
is  soft  (H.  =2)  and  its  sp.gr.  is  about  4.5.  It  fuses 
very  easily,  thin  splinters  being  melted  even  in  the 
flame  of  a  candle.  It  cleaves  easily  along  one  plane. 
When  heated  on  charcoal,  stibnite  yields  white 
fumes  of  antimony  oxide  (Sb2Os)  and  at  the  same  time 
the  choking  fumes  of  SO2.  The  former  cover  the  char- 
coal near  the  assay  with  a  white  coating.  Heated 
in  an  open  glass  tube,  S02  is  evolved  and  a  white 
sublimite  of  Sb2Os  is  deposited  on  the  cool  portions 
of  its  walls.  The  mineral  is  soluble  in  HNOs  with 
the  precipitation  of  a  white  or  yellow  powder  (Sb205). 


DESCRIPTION  OF  MINERALS  13 

Stibnite  may  be  distinguished  from  all  minerals 
but  the  sulphides  by  the  test  for  sulphur  (p.  146). 
From  the  sulphides  it  is  distinguished  by  its  easy 
cleavage  in  one  direction,  its  low  fusibility,  and  the 
white  fumes  evolved  by  heating  on  charcoal.  The 
mineral  it  most  closely  resembles  is  galena  (No.  9). 

Sfcibnite  occurs  in  quartz  veins  and  in  metallifer- 
ous veins  associated  with  lead,  zinc  and  mercury  ores. 

It  is  used  in  the  manufacture  of  safety  matches, 
percussion  caps,  fireworks,  and  as  an  ore  of  antimony. 

8.  Molybdenite  (MoS2)  bears  a  close  resemblance 
to  graphite  (No.  2).  It  is  black,  soft  and  sectile.  Its 
density  is  4.7.  Its  color  is  lead  black  and  its  streak 
greenish-black.  In  very  thin  plates  it  is  translucent 
with  a  greenish  tinge.  It  occurs  in  plates  that  cleave 
readily  into  thin  pieces  that  are  flexible. 

Molybdenite  is  infusible,  but  it  imparts  to  the  edges 
of  the  blowpipe  flame  a  yellowish-green  color.  It 
yields  all  the  reactions  for  sulphur  and  when  heated 
in  an  open  glass  tube  it  deposits  a  pale  yellow  sub- 
limate of  MoOs  on  the  cooler  portions  of  the  walls. 
The  mineral  is  decomposed  by  HNOs  with  the  pro- 
duction of  a  gray  powder  (MoOs) . 

Its  softness  and  color  distinguish  it  from  all  min- 
erals but  graphite  (No.  2)  and  some  forms  of  pyrolu- 
site  (No.  41).  From  these  it  is  easily  distinguished 
by  the  reactions  for  sulphur  (p.  163)  and  molybdenum 
(p.  160). 

Molybdenite  is  the  principal  ore  of  molybdenum, 
salts  of  which  are  used  in  the  chemical  laboratory  and 
for  imparting  a  green  color  to  porcelain.  The  metal 
is  used  in  an  alloy  (ferro-molybdenum)  for  hardening 
steel. 


MINERALS  AND  ROCKS 


The  mineral  occurs  as  grains  embedded  in  lime- 
stone and  crystalline  rocks  and  as  plates  and  irregular 
masses  in  quartz  veins. 

9.  Galena  (PbS)  is  the  principal  ore  of  lead.     It 


FIG.  7. — Galena  Crystals. 

is  found  in  large  and  small  isometric  crystals  that  are 
usually  cubic  or  octahedral  in  habit  (Fig.  7  and  Fig.  8), 
in  coarse  and  fine  granular  aggregates  and  in  great 
crystalline  masses.  It  is  lead  gray  in  color  and  has  a 


FIG.  8. — Galena  Crystals  on  Rock.     (After  U.  S.  Geol.  Survey.) 

grayish-black  streak.  Its  luster  is  metallic,  its  hard- 
ness about  2.5  and  its  sp.gr.  about  8.5.  It  is  charac- 
terized by  three  cleavages  perpendicular  to  one  an- 
other, which  yield  cubical  fragments. 


DESCRIPTION  OF  MINERALS  15 

Heated  on  charcoal,  galena  fuses,  yielding  sul- 
phurous fumes  and  a  globule  of  metallic  lead,  which 
may  easily  be  distinguished  from  silver  (No.  5)  by  its 
softness.  Near  the  assay  the  charcoal  is  coated  with 
a  yellow  sublimate  of  PbO.  Galena  is  soluble  in 
HNOs  with  the  separation  of  sulphur. 

Its  color  and  luster  distinguish  galena  from  all 
minerals  but  stibnite  (No.  7).  From  this  it  is  dis- 
tinguished by  its  more  difficult  fusibility,  by  its  cubi- 
cal cleavage  and  by  the  fact  that  it  does  not  yield 
white  antimony  fumes. 

Galena  is  found  in  veins  associated  with  quartz 
(No.  34),  calcite  (No.  50),  barite  (No.  63),  fluorite 
(No.  29)  and  sphalerite  (No.  10) ;  in  irregular  masses 
filling  crevices  in  limestone  and  in  other  less  common 
forms.  The  variety  that  occurs  in  veins  often  con- 
tains enough  silver  to  make  it  an  ore  of  this  metal. 

Galena  is  employed  in  glazing  common  stoneware, 
in  the  preparation  of  white  lead  and  other  pigments, 
and,  as  has  already  been  stated,  it  is  an  important  ore 
of  lead  and,  in  some  cases,  of  silver. 

10.  Sphalerite  (ZnS)  or  blende  is  the  principal 
ore  of  zinc.  It  occurs  in  handsome  isometric  crystals 
that  have  a  tetrahedral  habit  (Fig.  9),  in  grains  scat- 
tered through  limestones,  in  crusts  and  in  stalactitic 
and  globular  masses. 

Although  pure  zinc  sulphide  is  white,  most  sphaler- 
ite is  yellow  or  brown  and  translucent,  or  black  and 
nearly  opaque.  Its  streak  is  brown,  yellow  or  white. 
The  yellow  translucent  masses  look  like  rosin.  The 
luster  of  the  mineral  is  resinous,  its  hardness  3.5-4 
and  sp.gr.  about  4.  It  possesses  three  perfect  cleav- 
ages making  120°  with  each  other,  so  that  almost 


16  MINERALS  AND  ROCKS 

perfect  dodecahedrons  may  sometimes  be  split  from 
homogeneous  pieces. 

Sphalerite  is,  with  difficulty,  fusible.  When  heated 
on  charcoal,  it  volatilizes  slowly,  coating  the  coal  with 
a  yellow  sublimate  which  changes  to  white  upon 
cooling.  If  moistened  with  a  drop  of  dilute  cobalt 
nitrate  solution  and  heated  by  the  reducing  flame, 
the  white  sublimate  changes  to  green.  The  mineral 
dissolves  in  HC1,  yielding  sulphureted  hydrogen,  and 
gives  the  other  usual  tests  for  sulphur  (p.  146). 

Sphalerite  is  found  disseminated  through  limestone, 
and  in  streaks  and  veins  in  the  same  rock  and  in  veins 


FIG.  9. — Sphalerite  Crystals. 

in  siliceous  rocks.  It  is  often  associated  with  galena 
(No.  9),  chalcopyrite  (No.  17),  fluorite  (No.  29), 
barite  (No.  63)  and  silver  ores. 

The  mineral  is  used  in  the  manufacture  of  zinc 
white  (ZnO)  and  as  an  ore  of  the  metal. 

11.  Chalcocite  (Cu2S)  and  CoveUite  (CuS)  are 
important  copper  ores  in  some  places. 

Chalcocite  usually  occurs  in  black  masses  with 
a  dull  metallic  luster  and  in  a  black  sooty  powder,  in 
the  upper  portions  of  veins  of  copper  ores.  It  is 
found  also  in  crystals.  Its  hardness  is  2.5-3  and 
its  sp.gr.  about  5.7.  Its  streak,  like  its  color,  is 
black,  but  exposed  surfaces  are  often  tarnished  blue  or 
green. 


DESCRIPTION  OF  MINERALS  17 

12.  Covellite    or   indigo   copper   has  a  dark  blue 
color  on  fresh  fractures.     Its  streak  is  lead  gray  or 
black  and  its  luster  is  dull  or  metallic.     Its  hardness 
is  1.5-2  and  its, sp.gr.  about  4.6.     It  usually  occurs  in 
masses,  but  crystals  are  known. 

When  heated  in  the  open  glass  tube  or  on  charcoal, 
both  minerals  give  sulphurous  fumes.  When  mixed 
with  Na2C03  and  heated,  copper  globules  are  pro- 
duced. Both  minerals  dissolve  in  HNOs,  producing  a 
blue  solution  that  yields  the  tests  for  copper  (p.  146). 
When  heated  in  thin  splinters  by  the  blowpipe  flame, 
they  impart  to  it  a  green  color.  They  also  give  the 
copper  beads  (p.  141). 

They  are  distinguished  from  other  minerals  by  their 
color,  their  reactions  for  copper  and  the  absence  of  re- 
actions for  iron  (p.  138).  They  are  distinguished  from 
each  other  by  their  colors  on  fresh  fractures,  by  their 
sp.gr.,  and  the  fact  that  when  heated  on  charcoal 
covellite  ignites. 

13.  Cinnabar  (HgS)  is  the  only  compound  of  mer- 
cury that  occurs  in  sufficient  quantity  to  constitute  an 
ore. 

It  occurs  both  crystallized  and  in  granular 
masses.  It  is  cochineal-red,  inclining  to  brown,  in 
color  and  its  streak  is  scarlet.  It  is  opaque,  trans- 
lucent or  transparent,  has  a  hardness  of  2-2.5  and 
a  sp.gr.  of  8.  It  is  also  slightly  sectile. 

When  heated  gently  in  an  open  glass  tube,  it  yields 
S(>2  and  drops  of  mercury.  Before  the  blowpipe  on 
charcoal,  it  volatilizes  completely,  giving  off  SCb. 

It  is  easily  distinguished  from  all  other  minerals  by 
its  high  sp.gr.,  its  color  and  the  reactions  for  sulphur 
(p.  146).  Earthy  varieties  may  be  confused  with  red 


18  MINERALS  AND  ROCKS 

ocher  (No.  38),  but  the  reaction  on  charcoal  sufficiently 
distinguishes  them. 

Cinnabar  occurs  in  veins  cutting  volcanic  rocks 
and  neighboring  sedimentary  rocks. 

14.  Pyrite,  or  iron  pyrites  (FeS2),  Marcasite  (15.), 
white  pyrites  or  magnetic  pyrites  (FeS2),  and  Pyr- 


FIG.  ID. — Group  of  Cubic  Pyrite  Crystals. 

rhotite  (FenSn+i)  are  the  most  important  sulphides  of 
iron.  The  first  two  are  used  largely  in  the  manufac- 
ture of  sulphuric  acid. 


FIG,  11,— Pyrite  Crystals. 

Pyrite  and  marcasite  have  the  same  chemical  com- 
position (FeS2),  but  they  crystallize  in  different  sys- 
tems, the  former  usually  in  cubes  (Fig.  10),  octahedrons 
and  pyritoids  (Fig.  11),  and  the  latter  in  flat  crystals 
(Fig.  12),  often  forming  radiating  groups  that  may 
be  disk-like  or  globular. 


DESCRIPTION  OF  MINERALS  19 

Pyrite  is  one  of  the  commonest  of  all  minerals, 
being  found  in  a  great  variety  of  forms  under  very 
many  different  conditions.  It  frequently  occurs  in 
crystals  and  often  in  coarsely  granular  masses.  It 
has  a  metallic  luster,  a  bright  yellow  or  brassy  color, 
and  a  greenish  or  brownish-black  streak.  Its  hard- 
ness is  6-6.5  and  its  sp.gr.  about  5.  It  strikes  fire 
with  steel. 

In  the  closed  glass  tube,  it  gives  a  sublimate  of 
sulphur  and  a  magnetic  residue.  On  charcoal  before 
the  blowpipe,  it  ignites  and  burns  with  the  pale  blue 
flame  of  sulphur,  producing  S(>2.  When  treated  with 


FIG.  12. — Marcasite  Crystal  and  Group  of  Crystals. 

nitric  acid,  it  dissolves,  leaving  a  flocculent  residue 
of  sulphur. 

In  some  of  its  forms,  pyrite  resembles  gold  in  appear- 
ance; hence,  its  popular  name,  "fool's  gold".  It 
is  easily  distinguished  from  all  other  minerals  but 
marcasite  (No.  15)  and  chalcopyrite  (No.  17)  by  its 
color  and  brittleness,  and  from  chalcopyrite  by  its 
greater  hardness  and  the  absence  of  a  reaction  for 
copper.  It  cannot  be  distinguished  from  marcasite 
by  any  simple  means,  except  when  in  crystals. 

Pyrite  and  marcasite  are  mined  as  sources  of 
sulphur  for  use  in  the  manufacture  of  sulphuric  acid. 
After  driving  off  the  sulphur  by  roasting,  the  residue 
is  utilized  as  a  red  paint-pigment.  Often 


20  MINERALS  AND  ROCKS 

gold  is  mixed  with  the  pyrite,  when  the  mineral  be- 
comes a  source  of  the  precious  metal. 

When  exposed  to  the  air,  pyrite  rusts  and  changes 
to  limonite  (No.  45);  consequently,  veins  of  pyrite 
at  their  outcrops  are  often  marked  by  a  rusty  deposit 
of  limonite  and  other  oxidized  compounds,  known  as 
gossan. 

16.  Pyrrhotite  is  the  name  applied  to  a  series  of 
compounds,  the  composition  of  which  ranges  between 
FesSe  and  FeieSi?.  Usually  the  mineral  is  in  bronze- 
gray  granular  masses  that  tarnish  to  bronze  upon 
exposure  to  the  air.  Only  rarely  does  it  occur  in 
crystals.  Pyrrhotite  is  opaque  and  has  a  metallic 
luster.  Its  color  varies  between  bronze-yellow  and 
copper-red  and  its  streak  is  grayish-black.  Its  hard- 
ness is  a  little  less  than  4  and  its  sp.gr.  about  4.5. 
It  is  magnetic. 

Pyrrhotite  gives  the  usual  reactions  for  iron 
(p.  157)  and  sulphur  (p.  146)  and  sometimes,  in  addition, 
those  of  cobalt  and  nickel  (p.  160).  It  is  soluble  in 
HC1  with  the  evolution  of  H2S  which  may  easily  be 
detected  by  its  odor. 

It  is  easily  distinguished  from  all  other  minerals 
by  its  color,  its  magnetism  and  its  reaction  for  sul- 
phur. 

It  is  found  in  veins,  as  impregnations  in  various 
rocks  and  as  masses  enclosed  in  the  coarse-grained, 
dark,  igneous  rock,  known  as  norite.  It  is  mined 
in  a  few  instances  as  a  source  of  sulphur,  but  at  its 
principal  occurrence,  Sudbury,  Ont.,  it  is  mined  as  a 
source  of  nickel,  because  there  is  intermixed  with  it 
at  this  place  appreciable  quantities  of  pentlanditej 
which  is  (Fe,Ni)S. 


DESCRIPTION  OF  MINERALS  21 

17.  Chalcopyrite  (CuFeS2),  and  Bornite  (18.) 
(Cu3FeS3)  are  usually  regarded  as  copper  salts  of 
iron  acids — the  second,  as  a  salt  of  the  ortho-acid, 
H3FeS3,  and  the  first,  as  the  salt  of  the  derived  acid, 
HFeS2(H3FeS3-H2S=HFeS2).  Both  are  important 
ores  of  copper,  chalcopyrite  furnishing  the  greater 
part  of  the  commercial  metal. 

Chalcopyrite  (CuFeS2)  occurs  both  in  crystals 
and  massive.  Its  crystals  are  usually  elongated 
tetrahedrons  (Fig.  13). 

The  mineral  has  a  red-brass  color  and  a  greenish- 
black  streak.  Exposed  surfaces  are  often  tarnished 


FIG.  13.— Crystals  of  Chalcopyrite. 

with  an  iridescent  coating.  Its  hardness  is  3.5-4, 
and  its  sp.gr.  about  4.2. 

When  heated  on  charcoal,  chalcopyrite  fuses  to 
a  magnetic  globule.  When  heated  in  a  glass  tube, 
it  reacts  for  sulphur  (p.  146).  It  dissolves  in  HNO3, 
forming  a  green  solution  in  which  float  spongy  masses 
of  sulphur.  The  addition  of  ammonia  to  these  solu- 
tions changes  their  color  to  deep  blue  and  at  the  same 
time  causes  a  precipitation  of  foxy-red  ferric  hydroxide. 

From  the  few  other  brass-colored  minerals  chal- 
copyrite is  distinguished  by  its  inferior  hardness,  its 
streak  and  the  reactions  for  copper  (p.  146). 

The  mineral  occurs  in  veins  either  alone  or  asso- 
ciated with  other  compounds  of  copper  and  iron.  It 


22  MINERALS  AND  ROCKS 

is  also  frequently  associated  with  sphalerite  and  ga- 
lena (Nos.  10  and  9). 

It  is  an  abundant  ore  of  copper.  Much  of  the 
copper  obtained  from  it  contains  gold  or  silver  or 
both,  so  that  it  is  in  some  mines  an  important  source 
of  these  metals. 

18.  Bornite  or  horseflesh  ore  (CuaFeSs)  is  com- 
monly found  massive.  It  is  a  purplish-red  metallic 
mineral  with  a  grayish-black  streak.  Upon  exposure 
to  moist  air  it  becomes  covered  with  an  iridescent 
tarnish.  Its  hardness  is  about  3  and  its  sp.gr.  3. 

It  dissolves  in  HNOs  with  the  separation  of  sul- 
phur and  gives  the  usual  blowpipe  reactions  for  Cu, 
Fe  and  S.  When  its  solution  in  HNOs  is  treated  with 
an  excess  of  ammonia,  an  intense  purplish-blue  color 
results. 

Bornite  is  easily  distinguished  by  its  peculiar 
color  on  fresh  fracture  surfaces. 

It  is  usually  associated  with  other  copper  ores  in 
veins.  It  is  the  principal  ore  of  copper  in  many  South 
American  mines. 

ARSENIDES   AND    SULPH-ARSENIDES 

The  arsenides  and  sulph-arsenides  are  analogous  to 
the  sulphides.  In  the  latter,  a  portion  of  the  sulphur 
in  sulphides  may  be  regarded  as  being  replaced  by  As 
and,  in  the  former,  all  of  it.  These  compounds  when 
heated  before  the  blowpipe  give  off  voluminous  white 
fumes  that  have  a  characteristic  odor  which  is  usually 
described  as  resembling  that  of  garlic.  Analogous 
compounds,  containing  antimony,  when  heated,  also 
yield  voluminous  white  fumes,  but  they  are  without 
distinct  odor. 


DESCRIPTION  OF  MINERALS  23 

19.  Niccolite  (NiAs)  is  the  most  widely  distributed 
nickel  compound,  though  not  an  important  ore.     It 
usually  occurs  massive  as  the  filling  of  veins. 

It  is  opaque,  has  a  metallic  luster,  a  pale  copper-red 
color  and  a  brownish-black  streak.  The  surfaces  of 
nearly  all  specimens  are  tarnished  with  a  grayish 
coating.  Its  hardness  is  about  5  and  its  density  7.6. 

In  the  open  glass  tube  niccolite  yields  arsenic 
fumes  and  often  traces  of  SO  2.  When  fused  on  char- 
coal with  Na2COs,  it  yields  a  metallic  globule  which 
gives  the  reactions  for  nickel  (p.  160).  The  mineral 
dissolves  in  HNOa,  giving  an  apple-green  solution 
which  becomes  sapphire-blue  on  the  addition  of  an 
excess  of  ammonia. 

Niccolite  is  easily  distinguished  from  all  other 
minerals  by  its  color  and  its  reactions  for  nickel. 

It  occurs  principally  in  veins  associated  with  silver 
and  cobalt  arsenides  and  sulphides. 

20.  Cobaltite  (CoAsS)  and  (21.)  Smaltite  (CoAs2) 
are  the  two  most  important  ores  of 

cobalt.     They  are    both   silver-white 

in    color    and    have    a    grayish-black 

streak.     Both    occur  in  crystals  like 

those  of  pyrite  (No.  14),  more  often 

in  those  of  octahedral  habit  (Fig.  14),  FIG.  14. — Cobaltite 

and  in  granular  masses. 

Cobaltite  has  a  fairly  good  cubic  cleavage,  a  hard- 
ness of  5.5  and  a  sp.gr.  of  about  6.2. 

When  heated  in  the  open  glass  tube  it  gives  a  white 
sublimate  of  As2Os,  arsenic  fumes  and  S02  gas.  On 
charcoal  before  the  blowpipe,  it  yields  a  magnetic 
globule  which,  when  fused  with  borax  on  platinum 
wire,  gives  the  deep  blue  bead  of  cobalt  (p.  141). 


24  MINERALS  AND  ROCKS 

It  is  soluble  in  HNOs,  yielding  a  rose-colored  solution 
and  a  precipitate  of  sulphur. 

Smaltite  is  without  distinct  cleavage.  Its  hardness 
is  5  to  6  and  sp.gr.  6.3-7.  Its  reactions  in  the  glass 
tube  and  on  charcoal  are  like  those  of  cobaltite  except 
that  it  gives  off  no  SO 2.  It  is  soluble  in  HNOs  with 
precipitation  of  As2Os. 

The  two  minerals  are  distinguished  from  all  others 
by  their  color  and  their  reactions  for  cobalt  (p.  155). 
From  one  another  they  are  distinguished  by  the 
presence  or  absence  of  sulphur. 

Both  minerals  occur  in  veins.  On  the  surface  these 
veins  are  usually  marked  by  the  presence  of  rose- 
colored  erythrite  (No.  77),  which  coats  both  minerals 
wherever  they  are  exposed  to  the  action  of  moist  air. 

Cobalt  salts  are  used  in  the  manufacture  of  blue 
enamels,  blue  glass  and  blue  and  green  pigments. 

22.  Arsenopyrite  or  mispickel  (FeAsS)  is  the  most 
important  ore  of  arsenic.  It  is,  however,  not  of  great 
value,  since  most  of  the  arsenic  of  commerce  is  obtained 
as  a  by-product  (at  least  in  North  America)  from  the 
fumes  of  smelters  that  use  arsenical  copper  ores. 

Arsenopyrite  occurs  in  crystals 
(Fig.  15)  and  in  compact  and 
granular  masses.  It  is  a  silver- 

15 Arsenopyrite  white  metallic  mineral  closely  re- 
Crystals,  sembling  cobaltite  (No.  20)  and 
smaltite  (No.  21)  in  appearance,  but,  unlike  these, 
it  does  not  give  the  blue  bead  with  borax,  nor  is  it  in 
isometric  crystals. 

The  mineral  is  brittle,  but  it  has  one  good  cleavage. 
Its  hardness  is  5.5-6  and  its  sp.gr.  is  6.2.  Its  color  is 
silver-white  to  steel-gray  and  its  streak  grayish-black. 


DESCRIPTION  OF  MINERALS  25 

When  heated  in  the  closed  glass  tube,  arsenopyrite 
gives  a  red  sublimate  of  As2$3  and  later  a  black  mirror 
of  metallic  arsenic.  On  charcoal  it  gives  the  usual  reac- 
tions for  arsenic  (p.  151)  and  sulphur  (p.  146),  and  yields 
a  magnetic  residue.  The  mineral  yields  sparks  when 
struck  with  steel  and  gives  off  an  arsenic  odor.  It 
dissolves  in  HNOs  with  the  separation  of  sulphur. 

It  is  distinguished  from  cobaltite  and  smaltite 
(Nos.  20  and  21)  by  the  absence  of  cobalt. 

It  is  found  in  crystals  scattered  through  crystalline 
rocks  and  embedded  in  the  gangue  of  veins  and  as 
structureless  masses  filling  veins.  It  is  usually  associ- 
ated with  silver  and  lead  ores,  chalcopyrite,  pyrite, 
and  sphalerite  (Nos.  17,  14,  10). 

SULPH-ARSENITES   AND    SULPH-ANTIMONITES 

The  ortho-sulph-arsenites  are  salts  of  the  sulphur 
acid  As(SH)s  which  corresponds  to  the  oxygen  acid 
As(OH)a  or  HaAsOs.  The  ortho-sulph-antimonites 
are  salts  of  the  corresponding  antimony  acids.  Other 
sulpho  compounds  are  salts  of  acids  which  may  be 
regarded  as  derived  from  these. 

23.  Proustite  (AgsAsSs)  and  (24.)  Pyrargyrite 
(AgsSbSa)  are  two  important  ores  of  silver.  The 
former  is  known  also  as  light-ruby  silver  and  the  latter 
as  dark-ruby  silver.  Both  occur  as  complicated  crys- 
tals (Fig.  16)  in  veins  and  as  grains  mixed  with  other 
minerals,  forming  compact  masses.  Both  minerals  are 
gray  in  reflected  light  and  ruby-red  in  transmitted 
light.  Proustite  is  more  nearly  transparent  in  thin 
splinters  than  is  pyrargyrite  and  has  a  brighter  color. 
The  streak  of  proustite  is  bright  red  and  that  of  pyr- 


26  MINERALS  AND  ROCKS 

argyrite   purplish-red.     Their  hardness    is    2.5.     The 
sp.gr.  of  proustite  is  5.6  and  of  pyrargyrite  5.85. 

When  heated  in  the  closed  tube  proustite  fuses 
easily  and  gives  a  slight  reddish-yellow  sublimate  of 
As2S3.  Pyrargyrite,  under  the  same 
conditions,  yields  a  reddish-brown 
sublimate  of  antimony  oxy sulphide. 
When  fused  with  Na2COs  on  char- 
coal, both  give  a  globule  of  silver, 

FIG.  l&— Pyrargyrite    but  proustite  yields  the  white  gar- 
Crystals.  V   1        J?  /A  T-'l 

hcky  fumes  of  As,  while  pyrargyrite 
yields  odorless  fumes.  Both  give  the  ordinary  re- 
actions for  sulphur  (p.  146).  Both  minerals  dissolve 
in  HNOs  with  the  separation  of  sulphur  and,  in  the 
case  of  pyrargyrite,  with  the  precipitation  also  of  white 
Sb203. 

The  two  minerals  are  distinguished  from  all  others 
by  their  color  in  thin  splinters  and  their  reactions  for 
silver  and  sulphur.  They  are  distinguished  from  one 
another  by  their  streaks  and  the  reactions  for  As  or  Sb. 

Both  minerals  are  mined  with  others  as  silver  ores, 
especially  in  South  America  and  in  some  portions  of 
the  western  United  States. 

25.  Tetrahedrite  is  the  name  usually  given  to  a 
mixture  of  (Ag-Cu)gSb2S7  and  (Ag-Cu)sAs2S7.  The 
mineral  is  fairly  common  in  veins  carrying  silver  and 
copper  ores.  In  some  places  it  is  mined  as  a  source 
of  silver.  It  is  known  also  as  gray  copper  ore. 

Frequently,  tetrahedrite  occurs  in  tetrahedral  crys- 
tals (Fig.  17),  but  more  frequently  it  is  found  in  masses. 
Its  color  is  steel-gray  and  its  streak  steel-gray  or 
gray-black,  often  with  a  tinge  of  brown.  Its  luster 
is  metallic.  Its  hardness  is  3-4  and  sp.gr.  about  4.5. 


DESCRIPTION  OF  MINERALS  27 

When  heated  on  charcoal  or  in  the  open  glass 
tube,  both  the  arsenic  and  the  antimony  varieties 
yield  862  and  dense  white  fumes  which,  in  the  case 
of  the  antimony  varieties  (tetrahedrite),  have  no 
odor,  and,  in  the  case  of  the  arsenic  variety  (tennant- 
ite),  have  the  garlic  odor  of  arsenic  oxide.  Heated 
in  the  closed  tube,  the  mineral  fuses  and,  if  it  contains 
antimony,  gives  a  red  sublimate  of  antimony  oxy- 
sulphide,  or  if  an  arsenic  variety,  a  white  sublimate 
of  As2Sa  results.  Both  varieties  dissolve  in  nitric 


FIG.  17. — Tetrahedrite  Crystals. 

acid,  yielding  sulphur  and  a  solution  which  gives  the 
tests  for  copper  (p.  155).  In  the  antimonial  varieties 
there  is  also  a  separation  of  Sb2Os. 

Tetrahedrite  is  easily  recognized  by  its  crystals, 
its  color  and  hardness.  Massive  forms  are  distin- 
guished by  their  inferior  hardness  and  their  blowpipe 
reactions. 

CHLORIDES  AND   FLUORIDES 

Chlorides  and  fluorides  are  derived  from  HC1 
and  HF  by  the  replacement  of  hydrogen  by  metals. 

26.  Cerargyrite  (AgCl)  or  horn  silver  is  an  im- 
portant silver  ore  in  some  camps.  Although  occasion- 
ally occurring  in  cubical  crystals,  it  is  more  frequently 
found  as  waxy  masses  without  well-defined  structure. 


28 


MINEEALS  AND  ROCKS 


It  is  a  colorless,  white  or  gray  translucent  mass 
with  a  waxy  luster  and  a  white  streak.  Upon  exposure 
to  light,  it  tarnishes  to  brown,  violet  or  black.  Its 
hardness  is  1  to  1.5  and  sp.gr.  5.5.  It  can  be  cut 
into  shavings  with  a  sharp  knife  (is  sec  tile). 

In  the  closed  tube,  it  fuses  without  decomposi- 
tion. When  heated  on  charcoal,  it  yields  a  globule 
of  silver  and  when  heated  with  copper  oxide  in  the 
blowpipe  flame  it  gives  the  chlorine  reaction  (p.  146). 
It  is  insoluble  in  HNOs,  but  is  soluble  in  ammonia. 
From  this  solution  HNOs  throws  down  a  white  pre- 
cipitate. 

Cerargyrite  is  distinguished  by  its  sectility,  its 
waxy  luster  and  the  reactions  for  Ag  and  Cl. 

It  is  found  in  the  upper  portion  of  veins  contain- 
ing silver  ores. 

27.  Halite  (NaCl)  or  common  salt  is  the  best 
known  of  the  chlorides.  It  is  a  transparent  mineral 


FIG.  18.— Halite  Crystals. 

occurring   in   crystals   and   in   granular   or   compact 
masses. 

Its  crystals  are  usually  cubes,  often  with  depressed 
faces  (Fig.  18).  When  pure,  halite  is  colorless,  but 
the  impurities  often  present  color  it  red,  gray,  yellow 
or  blue.  Its  hardness  is  2.5  and  its  sp.gr.  2.3.  Its 
luster  is  vitreous.  It  is  readily  soluble  in  water  and 
possesses  a  salty  taste. 


DESCRIPTION  OF  MINERALS  29 

In  the  closed  glass  tube,  it  fuses  and  many  speci- 
mens decrepitate.  When  heated  before  the  blow- 
pipe, it  colors  the  flame  yellow.  If  a  small  quantity 
is  fused  on  a  platinum  wire  and  sprinkled  with  a  little 
powdered  copper  oxide,  and  then  heated  before  the 
blowpipe,  the  flame  will  become  bright  blue.  The 
mineral  easily  dissolves  in  water  and  its  solution  yields 
an  abundant  white  precipitate  with  silver  nitrate. 

Halite  is  easily  distinguished  from  other  soluble 
minerals  by  its  salty  taste;  the  yellow  color  it  imparts 
to  the  blowpipe  flame  and  the  reaction  for  chlorine. 

It  is  found  in  beds  interstratified  with  other  sub- 
stances deposited  from  water,  and  in  solution  in  the 
ocean,  salt  lakes  and  the  brines  saturating  certain 
limestones  and  sandstones. 

This  mineral  is  the  chief  source  of  sodium  com- 
pounds. It  is  employed  in  glazing  pottery,  in  enamel- 
ing, in  metallurgical  processes  and  many  more  familiar 
operations. 

28.  Sylvite  (KC1)  is   one  of   the   chief    sources  of 
potassium  salts.     It  is  like  halite  in  its  occurrence 
and  in  most  of  its  properties.     Its  hardness,  however, 
is  2  and  its  sp.gr.  1.99. 

When  heated  before  the  blowpipe,  it  imparts  a 
violet  tinge  to  the  flame,  which  can  be  detected  when 
masked  by  the  yellow  flame  of  sodium  by  viewing  it 
through  blue  glass.  Otherwise,  sylvite  and  halite 
react  similarly. 

It  is  distinguished  from  halite  by  the  violet  color 
it  imparts  to  the  flame. 

29.  Fluorite    (CaF),    fluorspar,   is    the    principal 
source  of  fluorine.     As  usually  found,  it  is  a  trans- 
parent mineral  that  is  characterized  by  its  fine  color 


30 


MINERALS  AND  ROCKS 


and    handsome    crystals.     It    occurs    also    granular, 
fibrous  and  massive. 

Fluorite  is  isometric.  Its  crystals  are  usually 
cubes,  octahedrons  or  combinations  of  both.  Fre- 
quently, the  cubes  are  intergrown  (Fig.  19).  The 


FIG.  19.— Fluorite  Crystals. 

mineral  is  transparent,  and  white,  yellow,  green, 
purple  or  red.  Its  streak  is  white,  its  luster  vitreous, 
and  its  cleavage  octahedral.  It  is  brittle.  Its  hard- 
ness is  4  and  sp.gr.  about  3.2. 

In  the  closed  tube,  fluorite  decrepitates  and  phos- 
phoresces. When  heated  on  charcoal  it  fuses,  colors 
the  flame  yellowish-red  and  yields  an  enamel-like 
residue  that  reacts  alkaline.  Its  powder,  treated  with 
H2S04,  yields  hydrofluoric  acid  (HF)  which  etches 
glass. 

Fluorite  is  easily  distinguished  from  all  other 
minerals  by  its  crystallization,  hardness,  cleavage 
and  the  reaction  for  fluorine  (p.  148). 

It  occurs  in  veins,  often  mixed  with  metallic  ores, 
and  as  crystals  on  the  walls  of  cavities  in  rocks. 

It  is  used  as  a  flux  in  smelting  iron  and  other  ores, 
in  the  manufacture  of  opalescent  glass  and  of  the 
enamel  used  on  cooking  utensils;  it  is  also  employed 
in  making  HF,  which,  in  turn,  is  used  in  etching  glass. 
The  brighter  colored  varieties  are  employed  in  cheap 
jewelry  and  as  an  ornamental  stone. 


DESCRIPTION  OF  MINERALS  31 

NITRATES 

The  two  most  important  nitrates  are  (30.)  Niter 
(KN03),  and  (31.)  Soda-niter  (NaN03).  The  first 
is  known  also  as  saltpeter  and  the  latter  as  Chile 
saltpeter. 

Both  are  colorless,  transparent  minerals  that  are 
soluble  in  water.  Both  occur  massive,  as  incrusta- 
tions and  as  the  cement  of  soil  grains.  Niter  is  also 
found  in  tufts  of  acicular  crystals.  Both  minerals 
have  a  hardness  of  about  2,  and  a  sp.gr.  of  2.1  to  2.25. 

Both  deflagrate  when  heated  on  charcoal  and  soda- 
niter  deliquesces  and  finally  liquefies.  They  both 
yield  the  tests  for  HNOs  (p.  161)  and  both  have  a 
cooling  taste.  Niter  colors  the  blowpipe  flame  violet 
and  soda-niter  imparts  a  yellow  tinge. 

The  two  minerals  occur  in  the  soil  of  rainless  or 
very  dry  regions  and  niter  in  the  soil  covering  the  floors 
of  caves. 

The  niters  are  used  in  the  production  of  HNOa 
and  io  the  manufacture  of  fertilizers  and  gunpowder. 

8OKATES 

The  two  borates  of  most  importance  are  (32.) 
Borax  (Na2B4O7-10H20),  and  (33.)  Colemanite 
(Ca2B6Oii-5H20).  Both  are  commercial  products. 

Borax  occurs  as  crystals  (Fig.  20),  as  a  crystalline 
cement  of  sand  grains  around  certain  salt  lakes,  and 
as  incrustations  on  the  surfaces  of  marshes  and  the 
sands  of  deserts. 

It  is  a  white,  gray  or  bluish  transparent  or  trans- 
lucent mineral  with  a  white  streak.  It  has  a  vitreous, 


32 


MINERALS  AND  ROCKS 


FIG.  20. — Borax 
Crystal. 


resinous  or  earthy  luster  and  is  brittle.  Its  hardness 
is  2-2.5  and  its  sp.gr.  1.7.  On  exposure  to  the  air, 
borax  loses  water  and  tends  to  become  white  and 
opaque.  The  mineral  is  soluble  in  water  and  has  a 
sweetish,  alkaline  taste. 

Before  the  blowpipe,  borax  puffs  and  fuses 
to  a  transparent  globule,  at  the  same  time  coloring 
the  flame  yellow.  When  moistened 
with  H2&04  and  heated,  the  flame 
becomes  tinged  with  green.  When 
dissolved  in  HC1,  its  solution  will 
turn  turmeric  paper  reddish-brown 
after  drying  at  100°.  When  the  stain 
is  moistened  with  ammonia,  it  changes 
to  black. 

Purified  borax  is  used  as  an  antiseptic  and  pre- 
servative in  medicine,  in  cosmetics  and  in  the  manu- 
facture of  enamels,  glazes  and  glass.     Most  of  the 
borax  used  in  the  arts  is  made  from 
colemanite. 

Colemanite  occurs  in  handsome 
crystals  (Fig.  21),  and  in  granular  and 
compact  masses. 

It  is  colorless,  milky-white,  yellow 
ish,  white  or  gray,  and  is  transparent 
or  translucent.  It  has  a  vitreous  luster 
and  a  white  streak.  Its  hardness  is 
4-4.5  and  its  sp.gr.  is  2.4. 

Heated  before  the  blowpipe,  it  decrepitates,  ex- 
foliates and  partially  fuses,  at  the  same  time  coloring 
the  flame  yellowish-green.  It  is  soluble  in  hot  HC1, 
but  upon  cooling  the  solution  a  voluminous  mass  of 
boric  acid  separates  as  a  gelatinous  precipitate. 


FIG.  21.— Cole- 
manite Crvstal. 


DESCRIPTION  OF  MINERALS 


33 


Colemanite  is  easily  distinguished  from  other  white, 
translucent  minerals  by  the  flame  test  and  the  gelati- 
nous precipitate  from  its  cooled,  hydrochloric  acid  solu- 
tion. It  is  best  distinguished  from  borax  by  its  in- 
solubility in  water  and  its  greater  hardness. 

The  mineral  occurs  in  layers  interstratified  with 
clay  and  gypsum  and  in  veins  cutting  lake  deposits. 

Colemanite  is  the  principal  source  of  the  boric  acid 
and  borax  used  in  the  arts. 

OXIDES 

The  mineral  oxides  may  be  regarded  as  compounds 
in  which  all  the  hydrogen  of  water  (H20)  has  been 
replaced  by  metals.  Hydroxides  may  be  regarded 
as  those  in  which  only  part  of  the  hydrogen  is  thus 
replaced. 

34.  Quartz  (Si02)  is  one  of  the  commonest  of  all 
minerals.  It  occurs  as  crystals  (Fig.  22)  and  crystal- 


FIG.  22. — Quartz  Crystals. 

line  masses,  in  veins,  as  grains  in  crystalline  rocks  and 
as  small  fragments  in  sand  and  sandstones.  It  is 
one  of  the  commonest  decomposition  products  of 
weathered  rocks. 

I  Quartz  is  transparent  and  colorless,  or  white,  when 
pure,  but  it  may  have  almost  any  color  when  impure. 


34  MINERALS  AND  ROCKS 

Its  crystals  are  hexagonal  prisms  terminated  by  trig- 
onal or  hexagonal  pyramids.  They  may  be  nearly 
equidimensional  or  they  may  be  elongated  into 
columnar  or  acicular  forms.  Its  hardness  is  7  and  its 
sp.gr.  2.65.  It  is  insoluble  in  all  ordinary  acids,  but  is 
vigorously  attacked  by  HF. 

It  is  infusible  before  the  blowpipe  and  does  not  react 
with  any  of  the  ordinary  reagents. 

It  is  distinguished  from  most  minerals  by  its  hard- 
ness and  from  the  few  other  equally  hard,  transparent 
ones  by  its  inf usibility  and  general  stability  toward 
reagents. 

Its  most  common  crystallized  varieties  are: 

Rock   crystal,    rhinestone,.  etc.,    a   transparent, 

colorless  phase. 
Amethyst,  violet  colored. 
Citrine,  or  false  topaz,  a  yellow  variety. 
Smoky   quartz,    or   cairngorm   stone,    a   smoky- 
brown  transparent  or  translucent  variety. 
Its  common  crystalline  varieties  are : 

Milky   quartz,   a  white   translucent   or  nearly 

opaque  variety. 
Chalcedony,  a  dense  translucent  variety,  with 

a  waxy  luster. 

Carnelian,  a  clear  red  or  brown  chalcedony. 
Chrysoprase,  an  apple-green  chalcedony. 
Plasma,  a  bright  green,  translucent  chalcedony. 
Heliotrope,  or  bloodstone,  a  plasma  dotted  with 

red  spots. 
Agate,  a  variegated  or  banded  chalcedony  or  a 

mixture  of  chalcedony  and  quartz. 
Onyx,   an    evenly   banded    agate,   showing    a 
marked  contrast  in  colors. 


DESCRIPTION  OF  MINERALS  35 

Sardonyx,  an  onyx  in  which  some  of  the  bands 

are  carnelian. 

Flint  and  jasper  are  very  fine-grained,  crystalline 
aggregates  of  gray  or  red  quartz. 

Crystallized  varieties  are  used  as  gems  and  also 
in  the  construction  of  optical  instruments  and  in  the 
manufacture  of  cheap  jewelry.  Milky  quartz  is  ground 
and  used  as  an  abrasive,  in  the  manufacture  of  sand- 
paper and  in  the  making  of  earthenware.  Quartz 
sand  is  utilized  in  making  glass,  and  in  the  form  of 
sandstone  it  is  used  as  a  building  stone.  Crushed 
quartz  is  also  employed  in  some  smelting  operations. 

35.  Cuprite  (Cu2O)  is  an  important  oxide  of  cop- 
per, but  not  a  common  ore  of  the  metal.     It  occurs  in 
isometric  crystals  which  have  octahedral 
(Fig.    23)    or    cubical    habits    and    in 
capillary,    earthy  and  granular   aggre- 
gates.    It  is  also  found  massive. 

It    is    opaque,   translucent  or  even 
transparent  in  different  specimens.     Its   FJG  23  ^,u  rite 
luster  may  be  vitreous  or  earthy  and          Crystal, 
its  color  is  red,  brown  and,  in  rare  cases, 
black  by  reflected  light  and  crimson  by  transmitted 
light.     Its  streak  is  brownish-red  and  it  has  a  brilliant 
luster.     When   rubbed   with   the   finger   it   becomes 
yellow  and  finally  green. 

Before  the  blowpipe,  cuprite  fuses  and  colors  the 
flame  green.  If  moistened  by  HC1  and  heated,  the 
color  of  the  flame  becomes  bright  blue.  Heated  on 
charcoal,  the  mineral  fuses  and  upon  long-continued 
heatinpr  yields  a  globule  of  copper.  It  dissolves  in 
strong  HC1,  forming  a  solution  which,  when  cooled 
and  diluted  with  water,  gives  a  white  precipitate  of 


36  MINERALS  AND  ROCKS 

Cii2Cl2.  It  also  gives  the  common  reactions  for  cop- 
per (p.  155). 

Cuprite  may  easily  be  distinguished  from  almost 
all  other  red  minerals  by  its  reactions  for  copper. 
Moreover,  it  is  harder  than  cinnabar  and  proustite 
and  softer  than  hematite  (Nos.  13,  23,  38). 

It  is  found  alone  or  associated  with  other  copper 
minerals  in  veins,  and  disseminated  as  tiny  grains  in 
certain  sedimentary  rocks. 

It  is  mined  with  other  minerals  as  an  ore  of  copper. 

36.  Zincite  (ZnO)  is  a  comparatively  rare  mineral, 
but  it  occurs  in  such  large  quantity  at  Franklin  Fur- 
nace, N.  J.,  that  it  is  utilized  as  an  ore  of  zinc. 

Zincite  is  only  occasionally  found  in  crystals.  It 
usually  occurs  massive  or  as  grains  in  limestone, 
associated  with  other  zinc  minerals. 

The  mineral  is  colorless  or  red  (in  consequence  of 
the  presence  of  manganese)  and  it  has  a  colorless  or 
an  orange  streak.  It  cleaves  easily  in  one  direction. 
Its  hardness  is  4-4.5  and  its  sp.gr.  about  5.5. 

When  heated  in  the  closed  tube,  the  red  variety 
of  zincite  blackens,  but  it  resumes  its  original  color 
upon  cooling.  With  the  borax  bead,  it  gives  the 
manganese  reaction  (p.  141).  Heated  on  charcoal,  it 
produces  a  white  coating,  which  turns  green  when 
moistened  with  cobalt  solution  and  heated  with  the 
oxidizing  flame  (p.  147).  It  is  soluble  in  acids. 

Red  zincite  is  not  easily  confused  with  other  min- 
erals. It  is  identified  by  its  color  and  the  reaction  for 
zinc. 

37.  Corundum  (A1203)  is  the  hardest  known  min- 
eral with  the  exception  of  diamond.     In  consequence 
of  its  great  hardness,  it  is  used  as  an  abrading  agent 


DESCRIPTION  OF  MINERALS  37 

under  the  name  of  emery.     It  also  furnishes  the  most 
valuable  of  the  gems. 

The  mineral  occurs  in  crystals  and  in  granular 
masses.  Its  crystals  are  pyramidal  or  barrel-shaped 
(Fig.  24),  and  are  usually  rough  with  rounded  edges. 
The  mineral  is  transparent  or  translucent,  has  a  glassy 
luster,  a  hardness  of  9  and  a  sp.gr.  of  4.  Its  color 
varies  from  white,  through  gray  to  various  shades  of 


FIG.  24. — Corundum  Crystals. 

red,  yellow  or  blue.     Some  specimens  are  colorless. 
Its  streak  is  uncolored. 

The  three  most  important  varieties  are: 

Corundum,  dull-colored  varieties  used  as  polish- 
ing material. 
Emery,  impure  black,  granular  variety,  used  as 

an    abrasive. 
Sapphire,    the    transparent,    colored    varieties 

which  are  used  as  gems. 

Jewelers  divide  sapphires  into  sapphires,  possessing 
a  blue  color;  rubies,  having  a  red  shade;  oriental 
emeralds,  oriental  topazes  and  oriental  amethysts, 
with  green,  yellow,  and  purple  tints. 

Powdered  corundum,  moistened  with  a  few  drops 
of  cobalt  nitrate  and  heated  for  a  long  time,  assumes 
a  blue  color.  The  mineral  gives  no  other  character- 
istic reactions.  It  is  infusible  and  insoluble. 


38  MINERALS  AND  ROCKS 

It  is  easily  characterized  by  its  hardness. 

Corundum  is  found  in  veins  and  scattered  through 
dike  rocks  and  granular  limestones. 

38.  Hematite  (Fe203)  is  the  principal  ore  of  iron. 
It  occurs  in  large,  brilliant  black  crystals  (Fig.  25) 
with  a  rhombohedral  habit,  in  yellow,  brown  and  red 
earthy  masses,  in  dense  black,  structureless  masses, 
in  granular  and  micaceous  aggregates  and  in  stal- 
actitic  forms. 

When  pure  and  massive,  or  in  crystals,  hematite 
is  black,  glistening  and  opaque,  except  in  very  thin 


FIG.  25. — Hematite  Crystals. 

splinters,  which  are  red  and  translucent.  Earthy 
varieties  are  red.  The  streak  of  all  varieties  is  brown- 
ish-red. The  hardness  of  crystallized  hematite  is 
5.5-6.5  and  its  density  5.2. 

The  mineral  is  infusible  before  the  blowpipe. 
In  the  reducing  flame  on  charcoal  it  becomes  magnetic. 
It  is  soluble  in  HC1. 

The  dark  varieties  are  easily  distinguished  by  their 
streak  and  the  fact  that  they  become  magnetic  after 
heating.  Red,  earthy  varieties  may  resemble  cinna- 
bar or  cuprite  (Nos.  13  and  35),  but  they  are  easily 
distinguished  from  these  by  the  absence  of  the  tests 
for  S  and  Cu. 

Several  varieties  have  received  special  names: 


DESCRIPTION  OF  MINERALS  39 

Specular  ore  is  an  aggregate  of  glistening  grains. 

Ocher  is  a  red,  earthy  kind. 

Clay  ironstone  is  a  hard  brown  or  red  impure 

variety  with  a  dull  luster. 

Oolitic  ore  is  a  red  mass  of  compacted  spherical 
or  nearly  spherical  grains  made  up  of  con- 
centric layers. 

Fossil  ore  is  a  mass  of  fragments  of  shells  com- 
posed of  red  hematite. 

Hematite  occurs  in  beds  and  irregular  deposits 
associated  with  sedimentary  rocks  and  as  crystals 
on  the  walls  of  clefts  in  volcanic  rocks,  and  in  veins. 

The  mineral  is  mined  as  an  ore  and  as  a  pigment 
under  the  name  of  red  ocher.  A  fibrous  variety  is 
cut  into  balls  and  cubes  for  use  as  jewelry  and  the 
powder  of  some  of  the  massive  forms  is  used  as  a  polish- 
ing powder. 

39.  Rutile  (Ti02)  occurs  in  small,  black  crystals 


FIG.  26.— Rutile  Crystals. 

(Eig.  26),  and  in  dark,  purplish-brown  or  black  masses. 
Its  crystals  are  prismatic  or  acicular,  and  all  are  verti- 
cally striated.  They  possess  one  perfect  cleavage. 
The  mineral  is  reddish,  yellowish-brown  or  black  by 
reflected  light  and  sometimes  deep  red  by  trans- 
mitted light.  Some  varieties  are  opaque  and  others 
translucent  or  transparent.  Its  streak  is  pale  brown, 


40  MINERALS  AND  ROCKS 

its  hardness  6-6.5  and  sp.gr.  about  4.2.  Two  other 
minerals,  brookite  and  octahedrite,  have  the  same 
composition  as  rutile,  but  they  crystallize  differently 
and  have  different  physical  properties.  In  some  of 
their  phases  they  resemble  rutile  in  general  appearance. 
Rutile  is  infusible  and  insoluble.  With  beads  it 
gives  the  reactions  for  titanium  (p.  141).  When  fused 
with  Na2COs  on  charcoal  and  the  resulting  mass  is 
dissolved  in  HC1,  the  solution  thus  obtained  becomes 
violet  when  heated  with  scraps  of  tin. 

Its  density,  infusibility  and  the  reaction  for  Ti 
characterize  the  mineral.  Some  of  the  reddish-brown, 
massive  varieties  resemble  garnet;  but  their  differ- 
ences in  cleavage  serve  to  distinguish  them. 

Rutile  is  used  to  impart  a  yellow  color  to  porce- 
lain and  to  give  an  ivory  tint  to  artificial  teeth.  It  is 
also  used  in  the  manufacture  of  ferro-titanium,  which 
is  employed  in  making  certain  grades  of  steel. 

40.  Cassiterite  (SnCb)  or  tinstone  is  the  only 
ore  of  tin.  It  is  found  as  rolled  gravel 
of  a  dark  brown  color  and  in  glistening 
black  crystals  occurring  in  veins  with 
topaz  (No.  91)  and  other  minerals.  It 
occurs  also  as  crystals  and  grains  in 
granites  near  veins  containing  the  min- 
eral. The  crystals  are  very  much  like 

those  of  rutile  (see  FiS*  26)'  but  some 
are  more  prismatic  in  habit  (Fig.  27). 

Its  color  is  dark-brown  or  black,  its  streak  white, 
gray  or  black,  and  its  luster  very  glistening.  The 
purest  specimens  are  transparent;  but  ordinary 
varieties  are  opaque.  Its  hardness  is  6.5  and  sp.gr. 
about  7.  It  is  only  slightly  affected  by  acids.  With 


DESCRIPTION  OF  MINERALS  41 

some  difficulty,  it  may  be  reduced  to  metallic  tin 
when  mixed  with  Na2COs  and  heated  intensely  on 
charcoal. 

It  is  most  easily  distinguished  from  other  minerals 
by  its  high  sp.gr.  and  its  inertness  when  treated  with 
reagents. 

The  three  varieties  commonly  recognized  are : 
Tinstone,  the  crystallized  or  massive  variety. 
Wood  tin,  botryoidal  or  globular  masses  with 

radial  structure,  and 
Stream  tin,  pellets  in  gravel. 

41.  Pyrolusite  (MnCb)  is  an  important  source  of 
manganese  compounds.  It  occurs  granular  or  in 
columnar  masses  of  radiating  fibers.  In  all  cases  it 
is  probably  an  alteration  product  of  other  manganese 
compounds. 

It  is  a  soft,  black,  opaque  mineral  with  a  hardness 
of  2  or  2.5  and  a  sp.gr.  of  4.8.  Its  luster  is  metallic 
and  its  streak  black. 

When  heated  in  the  closed  tube,  it  yields  a  small 
quantity  of  water.  With  the  beads  it  gives  the  usual 
reactions  for  manganese  and  when  fused  with  Na2COs 
it  gives  an  opaque,  green  enamel.  Heated  alone,  it  de- 
composes and  evolves  oxygen  (3MnO2  =  Mn3O4+O2). 
It  dissolves  in  HC1  with  the  evolution  of  chlorine 
(MnO2+4HCl  =  MnCl2+2H2O+Cl2). 

Pyrolusite  is  easily  distinguished  from  other  soft, 
black  minerals  by  its  reactions  for  manganese  (p.  159) 
and  from  other  manganese  compounds  by  its  inferior 
hardness. 

It  occurs  in  veins  associated  with  other  metallic 
compounds  and  intermingled  with  iron  ores  in  beds 
and  irregular  deposits. 


42  MINERALS  AND  ROCKS 

Pyrolusite  is  employed  to  neutralize  the  green 
color  given  to  glass  by  iron  compounds  and  to  impart 
brown,  black  and  violet  colors  to  pottery.  Some  of  its 
compounds  are  used  as  mordants  in  dyeing.  It  is 
also  the  principal  compound  by  the  aid  of  which  oxygen 
and  chlorine  are  produced.  Its  important  use  is  in 
the  manufacture  of  spiegeleisen,  which  is  added  to 
steel  employed  in  casting  car  wheels. 


HYDROXIDES 

42.  Opal  (Si02+aq)  is  an  amorphous  compound 
which  may  be  a  mixture  of  silica  and  silicon  hydroxide. 
Its  content  of  water  is  variable.  It  is  probably  a 
colloid.  It  occurs  in  massive  form,  in  globular  and 
stalactitic  masses  and  in  an  earthy  condition.  Certain 
varieties  are  used  as  gem  stones. 

When  pure,  opal  is  colorless  and  transparent. 
Usually  it  contains  traces  of  impurities  and  may  be 
gray,  red,  green  or  blue  and  translucent  or  opaque. 
The  play  of  colors  in  gem  opal  is  due  to  the  interference 
of  light  rays  reflected  from  the  sides  of  thin  layers  of 
opal  material  of  different  densities.  The  hardness  of 
opal  is  5.5-6.5,  and  its  sp.gr.  2.1. 

All  varieties  are  infusible  before  the  blowpipe  and 
all  become  opaque  when  heated.  When  boiled  with 
KOH  solution,  some  varieties  dissolve  easily  and 
others  very  slowly. 

Opal  is  distinguished  from  other  amorphous  sub- 
stances by  its  hardness,  infusibility  and  insolubility 
in  acids.  It  is  distinguished  from  chalcedony  by  the 
large  quantity  of  water  it  yields  upon  heating. 


DESCRIPTION  OF  MINERALS  43 

The  principal  varieties  are : 

Hyalite,  colorless,  transparent. 

Precious  opal,  transparent  and  exhibiting  a  play 

of  colors. 
Fire  opal,  a  precious  opal,  in  which  the  colors 

are  brilliant  yellow  and  red. 
Siliceous  sinter,   pulverulent   accumulations   of 
white,  translucent  or  opaque  masses  deposited 
from  the  waters  of  hot  springs. 
Tripoli     and     infusorial     earth,     pulverulent 
accumulations  in  which  opal  is  an  important 
constituent. 

Opal  occurs  in  deposits  around  hot  springs,  in 
veins  cutting  volcanic  rocks,  and  as-  nodules  embedded 
in  limestones  and  slates. 

Besides  its  use  as  a  gem,  opal  in  the  forms  of  tripoli 
and  infusorial  earth  is  employed  in  the  manufacture 
of  soluble  glass,  polishing  powders,  cements,  dynamite, 
and  is  used  as  a  wood  filler,  an  abrasive,  in  making 
paint,  and  in  manufacturing  filter  stone. 

43.  Brucite  (Mg(OH)2)  is  a  soft,  white  mineral, 
occurring  in  tabular  crystals  and  in  platy  masses. 
It  possesses  a  very  perfect  cleavage,  splitting  easily 
into  foliae  that  are  flexible.  It  is  colorless  or  white, 
inclining  to  bluish  or  greenish.  It  is  transparent  or 
translucent,  has  a  hardness  of  2.5  and  a  sp.gr.  of  2.4. 
Its  luster  is  pearly  on  cleavage  surfaces. 

Brucite  is  infusible  before  the  blowpipe.  In  the 
closed  glass  tube,  it  gives  off  water  and  the  powder 
left  reacts  alkaline.  When  moistened  with  solution 
of  cobalt  nitrate  and  heated,  it  becomes  pink.  The 
pure  mineral  is  completely  soluble  in  acids. 

Brucite  may  be  confused  with  gypsum  (No.  67), 


44  MINERALS  AND  ROOKS 

talc  (No.  105),  diaspore  and  some  micas.  It  is  dis- 
tinguished from  diaspore  and  mica  by  its  inferior  hard- 
ness; from  talc,  by  its  solubility  in  acids  and  from 
gypsum  (CaS04+2H2O)  by  the  test  for  sulphur 
(p.  146). 

44.  Bauxite  (A120(OH)4)  is  the  principal  ore  of 
aluminium.  It  occurs  in  concretionary,  or  oolitic, 
grains  (Fig.  28),  in  earthy,  clay-like  forms  and  massive, 


FIG.  28. — Oolitic  Form  of  Bauxite. 

usually  in  pockets  or  lenses  in  clay,  resulting  from  the 
alteration  of  limestone. 

The  mineral  is  white  when  pure;  but,  as  usually 
found,  is  gray,  yellow,  red  or  brown.  It  is  translucent 
to  opaque  and  has  a  colorless  or  very  light  streak  and 
dull  luster.  Its  hardness  varies  between  1  and  3  and 
its  sp.gr.  is  2.55. 

Before  the  blowpipe  bauxite  is  infusible.  It  yields 
water  at  a  high  temperature.  When  moistened  with 
a  few  drops  of  cobalt  nitrate  solution  and  heated,  its 
powder  turns  blue.  It  is  with  difficulty  soluble  in 
hydrochloric  acid. 


DESCRIPTION  OF  MINERALS  45 

Concretionary  forms  of  bauxite  are  easily  distin- 
guished by  their  appearance  and  the  blue  color  they 
give  with  cobalt  nitrate.  Earthy  forms  may  also  be 
recognized  by  the  blue  coloration  when  pure.  Impure 
varieties  can  be  detected  only  by  analysis. 

Bauxite  is  the  source  of  aluminium  in  the  manu- 
facture of  the  metal,  of  aluminium  salts,  of  alundum 
(artificial  corundum)  and  of  bauxite  brick  for  furnaces. 

45.  Limonite  (Fe403(OH)6)  or  brown  hematite  is 


FIG.  29. — Botryoidal  Group  of  Limonite  Fibers. 

one  of  the  important  ores  of  iron.  It  occurs  in  stalac- 
titic,  globular  (Fig.  29),  concretionary  and  earthy 
forms.  Another  mineral,  goethite,  resembles  limonite 
very  strongly.  Moreover,  it  contains  the  same  ele- 
ments as  does  limonite,  but  they  are  combined  differ- 
ently. Goethite  is  FeO  •  OH. 

Limonite  is  a  brown,  dull  or  earthy  mineral  with 
a  submetallic  luster  and  a  yellowish-brown  streak. 
Its  surface  is  often  black  and  varnish-like.  Its  hard- 
ness is  5.5  and  its  sp.gr.  about  3.8. 


46  MINERALS  AND  ROCKS 

When  heated  on  charcoal,  it  yields  a  magnetic 
residue.  In  the  closed  glass  tube,  it  gives  off  water  and 
is  changed  to  red  Y^Os.  It  reacts  with  the  beads 
for  iron  (p.  141)  and  easily  dissolves  in  HC1. 

It  is  distinguished  from  hematite  (No.  38)  by  its 
streak,  inferior  hardness,  and  its  reaction  for  water 
in  the  closed  tube,  and  from  goethite  (FeO-OH),  by 
its  lack  of  crystallization. 

Three  distinct  varieties  are: 

Yellow  ocher,  a  brownish-yellow,  earthy  type. 
Brown  clay  ironstone,  a  compact  variety  often  in 

concretionary  nodules,  and 
Bog  ore}  an  impure,  porous  variety,  containing 
stems  and  leaves,  found  in  the  bottoms  of 
ponds  and  marshes. 

Limonite  is  found  in  beds,  as  nodules  in  various 
rocks  and  as  crusts,  etc.,  resulting  from  the  alteration 
of  iron-bearing  minerals. 

ALUMINATES,   FERRITES   AND    CHROMITES 

The  minerals  belonging  to  this  group  are  usually 
regarded  as  oxides,  but  for  good  reasons  they  may 


FIG.  30.— Spinel  Crystals. 

also  be  considered  salts  of  metallic  acids.  Thus,  mag- 
netite (FesO^  may  be  looked  upon  as  the  iron  salt  of 
the  acid  FeO-OH,  thus  (FeO-O)2Fe;  chromite  as 
(CrO-0)2Fe;  spinel  as  a  magnesium  salt  of  A1O-OH, 


DESCRIPTION  OF  MINERALS  47 

thus  (AlO-O)2Mg;  and  franklinite  as  ((Fe,Mn)0-0)2 
(Fe,Zn,Mn). 

The  members  of  the  group,  which  is  known  as  the 
spinel  group,  commonly  crystallize  in  octahedrons, 
or  forms  with  octahedral  habits  (Fig.  30). 

46.  Spinel  (MgA^CU)  is  found  in  crystals,  and  in 
rolled  pebbles. 

It  is  colorless  when  pure,  but  is  usually  pink, 
blue,  brown,  yellow  or  black.  Its  hardness  is  8  and 
its  sp.gr.  3.5-3.6.  It  is  infusible,  but  frequently 
changes  color  upon  being  heated.  When  moistened 
with  Co(NO3)2  solution  and  heated,  it  becomes  blue. 
It  is  insoluble  in  HNOs  or  HC1,  but  is  slightly  soluble 
in  H2S04. 

The  special  named  varieties  are: 

Balas  ruby,  or  ruby  spinel,  a  clear,  red,  trans- 
parent variety. 
Ceylonite,  a  dark  green,  brown  or  black,  opaque 

variety. 
Picotite,  a  chrome  spinel.     It  is  yellowish  or 

greenish-brown  and  transparent. 
Spinel  is  easily  recognized  by  its  hardness,  color, 
and  the  shape  of  its  crystals. 

It  is  found  embedded  in  limestones,  serpentine, 
gneiss  and  occasionally  in  other  rocks.  It  is  some- 
times changed  to  talc,  muscovite  or  serpentine  (Nos. 
105,  96,  104). 

Transparent  spinels  are  used  as  gems. 

47.  Magnetite  (FeaOO  occurs  in  crystals  (Fig.  31) 
and   massive.     It    is   black,    has   a   black   streak,    a 
hardness    of    5.5-6    and    a    sp.gr.  of  4.9-5.2.     It  is 
strongly  attracted  by  a  magnet  and  in  many  instances 
it  exhibits  polar  magnetism. 


48  MINERALS  AND  ROCKS 

The  mineral  is  infusible  before  the  blowpipe.     Its 
powder  dissolves  slowly  in  HC1  and  the  solution  gives 
reactions  for  ferrous  and  ferric  iron. 

It  is  easily  recognized  by  its  color, 
crystallization,  and  magnetism. 

Magnetite  occurs  embedded  in  var- 
ious  rocks   and   as  the  principal  con- 
FIG.  31—  Magnet-  stituent  of  some  veins. 

ite  Crystal.  jt  jg  an  important  jron  Qre 

48.  Chromite  ((Fe,Cr)3O4)  closely  resembles  mag- 
netite, but  its  streak  is  brown  and  it  is  usually  non- 
magnetic.    Its  hardness  is  5.5  and  its  sp.gr.  4.5-4.8. 

The  mineral  alone  is  infusible  on  charcoal,  but 
when  mixed  with  Na2COs  and  heated  it  yields  a  mag- 
netic residue.  If  its  powder  is  fused  with  niter 
(No.  30)  and  the  fusion  treated  with  water,  a  yellow 
solution  of  K2CrO4  results.  It  gives  the  chromium 
reaction  with  the  beads  (p.  141). 

Chromite  is  easily  distinguished  from  magnetite 
(No.  47)  and  franklinite  (No.  49)  by  its  reaction  for 
chromium. 

It  occurs  as  crystals  and  grains  embedded  in  the 
rock  known  as  serpentine,  and  as  the  filling  of  little 
veins  cutting  it. 

The  mineral  is  the  sole  source  of  the  metal  chro- 
mium and  of  the  chrome-iron  alloy  employed  in  mak- 
ing chrome-steel. 

49.  Franklinite    ((Fe,Zn,Mn)3O4)    resembles  mag- 
netite in  general  appearance.     It  is  black  and  lus- 
trous   and    has    a    dark-brown    streak.     It    is    only 
slightly  magnetic.     Its  hardness  is  6  and  sp.gr.  5.2. 

It  is  infusible  on  charcoal,  but  yielclj  a  magnetic 
residue.  When  mixed  with  Na2COs  and  heated  on 


DESCRIPTION  OF  MINERALS  49 

platinum  in  the  oxidizing  flame,  it  gives  a  bluish- 
green,  opaque  bead  which  is  characteristic  for  man- 
ganese. If  the  mixture  is  heated  on  charcoal,  a  white 
coating  of  zinc  oxide  deposits  around  the  assay  and 
this  turns  to  green  when  moistened  with  Co(NOa)2 
and  again  heated. 

Franklinite  is  distinguished  from  magnetite  (No. 
47)  and  chromite  (No.  48)  by  its  reactions  for  Mn 
and  Zn. 

The  mineral  is  usually  in  crystals  or  grains  asso- 
ciated with  red  zincite  (ZnO),  (No.  36)  and  green  or 
pink  willemite  (ZnSiO4),  (No.  86). 

It  is  utilized  as  a  source  of  zinc,  zinc  oxide  and  is 
used  in  making  the  manganese  alloy,  spiegeleisen. 

CARBONATES 

The  carbonates  constitute  an  extremely  important 
group  of  minerals.  They  are  all  salts  of  the  acid 
H2CO3.  Most  of  them  are  normal  salts,  but  two 
important  carbonates  are  basic  salts.  Some  are  anhy- 
drous and  others  contain  water  of  crystallization. 
All  carbonates  effervesce  when  their  powder  is  treated 
with  hot  HC1,  due  to  the  evolution  of  the  gas  €62, 
and  the  basic  ones,  when  heated  in  a  glass  tube,  give 
off  water. 

Normal  Carbonates 

The  normal  anhydrous  carbonates  are  divided  into 
two  groups,  of  which  the  first  comprises  minerals 
which  crystallize  in  rhombohedrons,  scalenohedrons 
and  prisms  belonging  to  the  hexagonal  system,  and 
the  second  in  prisms,  pyramids  and  other  forms  that 
are  orthorhombic.  (Compare  Figs.  32  and  36.) 


50 


MINERALS  AND  ROCKS 


50.  Calcite  (CaCOs)  is  one  of  the  commonest 
minerals  and  one  of  the  most  handsomely  crystallized. 
Its  crystals  are  rhombohedrons  of  various  kinds, 
scalenohedrons  and  prisms  combined  with  rhombo- 


FIG.  32. — Calcite  Crystals. 

hedrons  (Figs.  32  and  33).  The  mineral  occurs  also 
as  stalactites  (Fig.  34),  in  pulverulent  masses,  in  radial 
and  fibrous  groups  and  in  granular  aggregates.  The 


FIG.  33. — Crystals  of  Calcite  Attached  at  One  End. 

latter  are  found  in  very  large  rock  masses,  known  as 
limestone  and  marble. 

Calcite  is  colorless  when  pure  and  transparent. 
More  frequently,  however,  it  is  white  or  some  light- 
colored  shade  and  translucent.  Its  streak  is  white 
and  its  luster  vitreous.  Its  hardness  is  3  and  sp.gr. 
2.71.  Its  cleavage  is  so  perfect  that  the  mineral 


DESCRIPTION  OF  MINERALS  51 

easily  breaks  into  little  rhombohedrons.     It  is  strongly 
double-refracting. 

Its  varieties  are  as  follows: 

Iceland  spar  is  colorless  and  transparent.  It 
usually  exhibits  clearly  its  strong  double 
refraction. 

Satin  spar  is  finely  fibrous. 
Limestone  is  a  granular  aggregate. 
Marble  is   a   limestone   which   exhibits,   when 


FIG.  34.— Stalactite  of  Calcite. 

broken,   the  glistening  cleavage  surfaces  of 
fractured  crystals. 

Stalactites  are  cylinders  or  cones  composed  of 
radial  fibers. 

Mexican  onyx  is  a  banded  crystalline  mass  of 
calcite  which  is  a  portion  of  a  large  stalactite. 

Travertine  is  a  deposit  of  white  or  yellow  por- 
ous calcite,  produced  by  deposits  from  water, 
often  around  organic  material,  like  the  blades 
or  roots  of  grass. 

Chalk    is    a    fine-grained,    pulverulent    calcite 

occurring  in  beds. 

Before  the  blowpipe  calcite  is  infusible;  but  many 
specimens  decrepitate.     It   colors  the  flame  reddish- 


52  MINERALS  AND  ROCKS 

yellow,  and,  after  heating,  the  residue  reacts  alkaline. 
The  mineral  dissolves  in  cold  HC1  with  the  evolution 
of  CO2. 

Calcite  is  easily  distinguished  from  all  other 
minerals  by  its  easy  cleavage  and  its  solubility  with 
effervescence  in  cold  HC1.  Its  massive  varieties  are 
distinguished  best  from  massive  dolomite  (No.  51), 
by  the  cold  HC1  reaction  and  from  massive  aragonite 
(No.  56)  by  heating  its  powder  with  a  little  Co(NO3)2 
solution.  Aragonite  becomes  lilac-colored,  while  cal- 
cite  remains  unchanged. 

Calcite  is  widely  distributed  in  beds,  in  veins  and 
in  loose  deposits  at  the  bottoms  of  springs,  lakes  and 
rivers. 

It  is  employed  in  the  construction  of  optical  instru- 
ments; in  the  manufacture  of  lime  and  cement,  and 
as  a  flux  in  smelting  operations.  It  is  one  of  the  ingre- 
dients in  glass-making.  Calcite  rocks  are  widely  used 
as  building  and  ornamental  stones. 

51.  Dolomite    ((Ca,Mg)CO3)   resembles  calcite  in 
most  of  its  properties.     Its  crystals,  however,  nearly 
always  show  curved  faces  (Fig.  35),  and  often  exhibit  a 
pearly  luster.     Its  hardness  is  3.5  to  4  and  its  sp.gr.  2.8. 

Dolomite  behaves  like  calcite  before  the  blowpipe, 
but  it  effervesces  with  cold  HC1  only  when  in  the 
finest  powder.  In  hot  acid  it  dissolves  easily. 

Dolomite  is  easily  distinguished  from  calcite  by  its 
greater  hardness  and  its  insolubility  in  cold  acid. 

The  mineral  occurs  in  the  same  forms  as  calcite. 
Rock  masses  composed  of  dolomite  are  known  either 
as  dolomite  or  as  magnesian  limestone. 

52.  Magnesite    (MgCOs)   is   also   very  much  like 
calcite,  but  crystals  are  comparatively  rare.     More- 


DESCRIPTION  OF  MINERALS  53 

over,  the  mineral  is  usually  opaque  or  translucent.  Its 
hardness  is  about  4  and  its  sp.gr.  3.1. 

Magnesite  behaves  like  calcite  before  the  blow- 
pipe. It  effervesces  in  hot  HC1  and  readily  yields  the 
magnesium  reaction  with  Co(NOa)2  (p.  147). 

It  is  easily  distinguished  from  calcite  by  its  sp.gr. 
and  by  the  fact  that  it  does  not  effervesce  readily 
with  cold  HC1.  It  differs  from  calcite  (No.  50)  and 


FIG.  35. — Dolomite  Crystals  on  Limestone. 

dolomite  (No.  51)  uf  that  it  does  not  color  the  blow- 
pipe flame  with  the  yellow-red  tint  of  calcium. 

Magnesite  usually  occurs  in  veins  and  masses 
associated  with  serpentine  (No.  104). 

It  is  employed  largely  in  the  manufacture  of  bricks 
that  are  used  for  lining  converters  in  steel  works,  etc. 
It  is  used  also  in  the  manufacture  of  paper  from  wood 
pulp;  in  making  artificial  marble,  etc.;  in  the  prepara- 
tion of  epsom  salts,  magnesia  and  other  medicinal 
products ;  and  in  the  manufacture  of  the  carbon  dioxide 
used  in  making  soda  water. 


54  MINERALS  AND  ROCKS 

53.  Siderite  (FeCOs)  was  formerly  an  important 
iron  ore.     It   is  found   crystallized   and  massive,   in 
botryoidal  and  globular  forms,  in  nodules  and  in  earthy 
masses.     Its  crystals  are  usually  rhombohedrons. 

Siderite  is  occasionally  white;  but  more  frequently 
is  yellow  or  brown  and  when  it  contains  manganese 
is  pink.  It  is  translucent  or  opaque.  Its  hardness  is 
3.5  and  sp.gr.  3.8. 

When  heated  in  the  closed  tube,  it  decrepitates, 
blackens  and  becomes  magnetic.  When  heated  on 
charcoal,  it  leaves  a  magnetic  residue.  Its  powder 
dissolves  very  slowly  in  cold  acids,  but  effervesces 
briskly  in  hot  ones. 

It  is  distinguished  from  the  other  carbonates  by 
its  reactions  for  iron,  its  color  and  its  sp.gr.  It  is 
most  easily  confused  with  rhodochrosite  (No.  55), 
but  the  two  minerals  are  differentiated  by  the  test  for 
manganese  (p.  159). 

The  mineral  is  found  in  veins  accompanying  metallic 
ores;  and  in  nodules  (ironstone  or  spathic  iron)  in 
clay  and  coal  shales. 

It  is  worked  as  an  ore  of  iron. 

54.  Smithsonite   (ZnCOs)    or   dry-bone  ore  is  an 
important  ore  of  zinc.     It  occurs  as  druses,  or  coatings 
of. tiny  crystals,  as  botryoidal  and  stalactitic  masses, 
as    granular    aggregates    and    as    friable    earth.     Its 
crystals  are  commonly  tiny  rhombohedrons. 

The  mineral  is  white,  gray,  green  or  brown.  It  has 
a  white  streak,  a  vitreous  luster,  a  hardness  of  5  and  a 
sp.gr.  of  4.4.  It  is  transparent  or  translucent. 

When  heated  in  the  closed  glass  tube,  CCb  is  driven 
off,  leaving  zinc  oxide  as  a  yellow  residue,  becoming 
white  on  cooling.  It  is  infusible,  but  if  moistened  with 


DESCRIPTION  OF  MINERALS  55 

Co(NO3)2  solution  and  heated  in  the  oxidizing  flame, 
it  becomes  green.  When  heated  on  charcoal,  a  dense 
white  vapor  is  produced.  This  settles  on  the  cool  parts 
of  the  charcoal  as  a  yellow  coating,  changing  to  white 
upon  cooling.  If  this  be  moistened  with  Co(N03)2 
and  heated  by  the  oxidizing  flame,  its  color  changes 
to  green. 

The  reactions  for  zinc  and  its  effervescence  in  hot 
acids  distinguish  smithsonite  from  all  other  compounds. 

The  mineral  occurs  in  beds  and  veins  in  limestone 
and  as  crusts  on  other  zinc  minerals,  and  as  porous 
masses  on  massive  smithsonite  (dry-bone  ore).  It 
is  nearly  always  associated  with  galena  (No.  9)  and 
sphalerite  (No.  10). 

It  is  mined  together  with  other  zinc  compounds  as 
an  ore  of  zinc. 

55.  Rhodochrosite  (MnCOs)  differs  from  the  other 
carbonates  in  its  rose-red  color  when  pure.  It  occurs 
in  rhombohedral  crystals,  in  cleavable  masses  and  in 
granular  aggregates.  It  is  rose-red  or  brown,  and 
transparent  or  translucent,  and  has  a  white  streak  and 
a  vitreous  luster.  Its  hardness  is  4  and  its  density  3.5. 

The  mineral  is  infusible  before  the  blowpipe,  but 
when  heated  it  decrepitates  and  changes  color.  When 
heated  on  charcoal  its  residue  is  usually  magnetic. 
When  treated  in  the  borax  bead,  it  colors  the  bead 
violet,  and  when  fused  with  Na2COs  on  charcoal  it 
yields  a  bluish-green  manganate. 

Pure  rhodochrosite  is  easily  distinguished  from  all 
other  minerals  but  the  manganese  silicate,  rhodonite, 
by  its  color  and  its  reaction  for  manganese  (p.  159). 
It  is  distinguished  from  rhodonite  by  its  effervescence 
with  hot  acids.  Impure  varieties  resemble  some  forms 


56 


MINERALS  AND  ROCKS 


of  siderite  (No.  53) ;  but  the  two  are  differentiated  by 
the  manganese  reaction. 

Rhodochrosite  occurs  in  veins  with  metallic  ores. 

It  is  used  to  a  slight  extent  as  an  ornamental  stone 
and  as  an  ore  of  manganese. 

56.  Aragonite  (CaCO3)  has  the  same  empirical 
formula  as  calcite  (No.  50),  but  it  crystallizes  in  the 
orthorhombic  system,  either  in  acicular  or  tabular 
crystals  (Fig.  36)  or  in  several  crystals  grouped  together 
(twinned)  in  such  a  way  as  to  resemble  hexagonal 


FIG.  36. — Aragonite  Crystals.          FIG.  37. — Twinned  Aragonite. 

prisms  (Fig.  37).  It  occurs  also  in  globular  masses 
in  divergent  bundles  of  fibers,  in  crusts,  in  stalactites 
and  in  massive  forms. 

The  mineral  has  two  cleavages.  It  is  white, 
gray,  green  or  some  other  light  shade,  and  is  trans- 
parent or  translucent.  It  has  a  white  streak  and  a 
vitreous  luster.  Its  hardness  is  3.5  to  4  and  sp.gr. 
about  2.95. 

Before  the  blowpipe,  aragonite  whitens  and  falls  to 
pieces;  otherwise,  its  reactions  are  like  those  of  calcite. 

It  is  distinguished  from  calcite  (No.  50)  by  its 
cyrstallization,  its  cleavage,  its  sp.gr.,  and  the  reac- 
tion with  Co(NO3)2  (p.  52). 


DESCRIPTION  OF  MINERALS  57 

The  mineral  occurs  in  beds  with  gypsum  (No.  67) 
and  as  deposits  from  hot  water. 
It  has  no  important  uses. 

57.  Strontianite   (SrCOs),  in  general  appearance, 
resembles  aragonite  (No.  56).     It  is  found  in  acicular 
crystals,  but  more  frequently  in  granular  aggregates 
and  massive. 

It  is  white  or  some  light  shade,  and  is  transpar- 
ent or  translucent.  Its  hardness  is  3.5-4  and  sp.gr. 
3.7. 

Before  the  blowpipe,  it  swells  and  colors  the 
flame  crimson.  It  dissolves  in  HC1,  giving  a  solution 
from  which  a  few  drops  of  H2S04  throws  down  a  white 
precipitate,  which  imparts  a  crimson  color  to  the 
blowpipe  flame. 

Strontianite  is  distinguished  from  all  minerals 
but  the  carbonates  by  its  effervescence  in  hot  HC1, 
and  is  distinguished  from  the  other  carbonates  by  the 
color  it  imparts  to  the  blowpipe  flame. 

It  is  the  most  common  of  all  strontium  compounds, 
and  is  the  principal  source  of  the  strontium  salts 
used  in  the  arts.  These  are  employed  in  refining 
beet  sugar  and  in  the  preparation  of  "  red  fire". 

The  mineral  occurs  as  veins  in  limestone  and  as 
an  alteration  product  of  other  stronium  compounds. 

58.  Witherite   (BaCOs)   is  similar  to   Strontianite 
in   appearance,    but   its   crystals   are   more   common 
(Fig.   38).     It  is  much  heavier,   however,   its   sp.gr. 
being  4.3.     Its  hardness  is  3  to  4. 

The  mineral  dissolves  in  hot  HC1.  From  this 
solution,  H2S04  throws  down  a  white  precipitate, 
which,  when  heated  in  the  blowpipe  flame,  imparts 
to  it  a  yellowish-green  color. 


58  MINERALS  AND  ROCKS 

Witherite  is  distinguished  from  the  other  car- 
bonates by  its  sp.gr.  and  the  green  color  it  imparts 
to  the  blowpipe  flame,  especially  after  moistening 
with  HC1. 

It  occurs  mainly  as  veins  in  limestone. 

It  is  a  source  of  barium  compounds,  but  is  com- 
paratively unimportant. 

59.  Cerussite  (PbCOs),  a  minor  lead  ore,  occurs 
in  crystals  and  in  fibrous  and  granular  masses.  Its 


FIG.  38. — Wither-        FIG.  39. — Cerus-  FIG.  40. — Group  of 

ite  Crystal  site  Crystals.  Cerussite  Crystals. 


simple  crystals  are  prismatic  (Fig.  39)  or  tabular 
and  these  are  often  grouped  into  bundles  (Fig.  40) 
so  as  to  produce  six-rayed  stars. 

The  mineral,  when  fresh,  is  white  and  vitreous, 
but  its  surface  is  frequently  discolored'  by  dark  de- 
composition products.  Its  streak  is  white,  its  hard- 
ness 3-3.5  and  its  sp.gr.  6.5. 

Cerussite  is  not  easily  confused  with  other  minerals. 
It  is  well  characterized  by  its  high  sp.gr.  and  its  reac- 
tions for  lead  (p.  158).  It  is  distinguished  from  angle- 
site  (No.  65)  by  its  effervescence  with  hot  HC1. 

Cerussite  is  found  with  other  lead  compounds  in 
veins.  It  often  coats  galena  (No.  9). 


DESCRIPTION  OF  MINERALS  59 

It  is  mined  with  galena  and  other  lead  minerals 
as  an  ore  of  lead. 

Basic  Carbonates 

60.  Malachite  ((CuOH)2C03),  and  azurite 
(Cu (CuOH)2(C03)2),  are  basic  copper  carbonates. 
Malachite  is  bright  green  and  azurite  bright  blue. 

Malachite  occurs  in  fibrous,  radiate,  stalactitic, 
granular  or  earthy  masses,  or  as  druses  of  small  crys- 
tals covering  other  copper  minerals. 

It  is  bright  green  in  color  and  has  a  light  green 
streak.  It  possesses  a  vitreous  luster,  but  this  becomes 
silky  in  fibrous  masses  and  dull  in  massive  specimens. 
Crystals  are  translucent  and  massive  pieces  opaque. 
Its  hardness  is  3.5-4  and  its  density  about  4. 

Malachite  is  fusible  before  the  blowpipe.  Heated 
with  Na2C03  it  yields  copper  globules  and  tinges  the 
flame  green,  but  if  moistened  with  HC1  the  color 
of  the  flame  becomes  azure-blue.  When  heated  in 
the  closed  tube,  it  gives  an  abundance  of  water.  It 
dissolves  in  hot  HC1  with  effervescence,  producing  a 
solution  which  becomes  purplish-blue  on  addition 
of  an  excess  of  (NH2)OH. 

Malachite  is  easily  distinguished  from  all  other 
minerals,  but  some  varieties  of  turquoise  (No.  78) 
and  atacamite  (Cu2(OH)3Ol),  by  its  color.  From 
these  it  is  distinguished  by  its  effervescence  with 
acids. 

The  mineral  is  a  decomposition  product  of  other 
copper  compounds.  It  occurs  in  the  upper  portions 
of  veins  of  copper  ores,  where  it  is  associated  with 
azurite  (No.  61),  copper  (No.  4),  cuprite  (No.  35), 
limonite  (No.  45)  and  the  sulphides  of  iron  and  copper. 


60  MINERALS  AND  ROCKS 

It  is  mined  with  other  copper  compounds  as  an 
ore  of  the  metal.  Massive  and  fibrous  forms  are 
employed  as  ornamental  stones  for  inside  decoration, 
and  are  sawn  into  slabs  and  polished  for  use  as  table 
tops,  clock  cases,  etc. 

61.  Azurite     (Cu(CuOH)2(C03)2)  is    more  •  often 
found  in  crystals  than  is  malachite.      It  occurs  also 
as  incrustations  and  in  massive  and  earthy  forms, 
associated  with  malachite. 

The  mineral  is  dark-blue,  vitreous  and  translucent 
or  transparent.  Its  streak  is  light  blue.  It  is  brittle 
and  has  a  hardness  of  3.5-4  and  a  sp.gr.  of  3.8. 

Its  blowpipe  and  other  characteristic  reactions 
are  the  same  as  those  for  malachite.  By  these  it  is 
easily  distinguished  from  all  other  blue  minerals. 

Azurite  is  associated  with  malachite  in  all  of  its 
various  types  of  occurrence. 

Its  uses  are  the  same  as  those  of  the  green  carbonate. 

SULPHATES 

The  sulphates  of  greatest  importance  are  those 
of  the  alkaline  earths  and  lead.  Of  these,  three  are 
anhydrous  and  one  is  hydrous.  All  yield  the  sulphur 
reaction  with  NaCO3  (p.  146). 

Anhydrous  Sulphates 

62.  Anhydrite    (CaS04)   rarely  occurs  in  crystals. 
It  is  usually  in  granular,  fibrous,  and  lamellar  masses 
of  a  white,  gray,  bluish  or  reddish  color,  and  a  white 
streak.     It  is  translucent  or  opaque  and  has  a  vitre- 
ous or  pearly  luster.     Its  hardness  is  3-3.5  and  sp.gr. 
2.9-2.98,  and  it  cleaves  in  three  perpendicular  direc- 
tions. 


DESCRIPTION  OF  MINERALS  61 

Before  the  blowpipe,  anhydrite  fuses  to  a  white 
enamel  and  colors  the  flame  red.  When  fused  with 
soda  on  charcoal  for  a  long  time,  it  forms  a  sulphide 
which  stains  silver.  It  is  slowly  dissolved  in  acid.  In 
the  presence  of  moisture,  it  gradually  changes  to 
gypsum  (No.  67). 

Anhydrite  is  distinguished  from  most  other  white 
and  light-colored  minerals  by  the  reaction  for  S  and 
the  red  color  it  imparts  to  the  flame.  It  is  differ- 
entiated from  celestite  (No.  64)  by  its  sp.gr. 

The  mineral  occurs  in  beds  with  rock  salt,  lime- 
stone and  gypsum. 

When  cut  and  polished  it  is  used  as  an  ornamental 
stone.  It  is  mixed  with  gypsum  and  used  as  land  plaster. 


FIG.  41.— Barite  Crystals. 

63.  Barite  (BaS04)  or  heavy  spar  usually  occurs 
in  crystals,  though  it  is  also  found  massive  and  in  gran- 
ular, fibrous  and  lamellar  forms. 

Its  crystals  are  usually  tabular  or  prismatic  (Fig. 
41)  and  they  possess  two  good  cleavages. 

The  mineral  is  white,  yellow,  brown,  blue  or  red; 
its  streak  is  white  and  its  luster  vitreous.  It  is  trans- 
parent or  opaque  and  brittle.  Its  hardness  is  3  and 
sp.gr.  4.5. 


62  MINERALS  AND  ROCKS 

Before  the  blowpipe,  barite  decrepitates  and  fuses, 
at  the  same  time  coloring  the  flame  yellowish-green. 
The  fused  mass  reacts  alkaline  to  litmus  paper.  When 
heated  with  Na2C03  on  charcoal  for  some  time,  the 
fused  mass,  placed  on  silver  and  moistened  with  a  drop 
of  water,  produces  a  black  stain.  The  mineral  is 
insoluble  in  water  and  acids. 

It  is  distinguished  from  all  other  minerals  by  its 
high  sp.gr.,  its  reaction  for  sulphur,  and  the  color  it 
imparts  to  the  blowpipe  flame. 

Barite  is  a  common  vein  stone  associated  with 
copper,  lead  and  silver  ores.  It  occurs  also  as  nodules 
in  clay  produced  by  the  weathering  of  limestone. 

The  white  varieties  are  ground  and  used  as  pig- 
ments. They  are  also  employed  in  the  manufacture 
of  paper,  oilcloth,  enameled  ware,  in  refining  sugar 
and  in  the  manufacture  of  barium  salts.  The  colored, 
massive  varieties  are  sawed  into  slabs  and  used  as 
ornamental  stones. 

64.  Celestite  (SrS04)  occurs  in  tabular  or  prismatic 
crystals  (Fig.  42),  and  in  fibrous 
and  in  globular  masses. 

The   mineral  is  usually   white 
and    transparent    or    translucent, 
but  sometimes  it  has  a  light  blue 
FIG.  42.— Celestite       tinge.     It  possesses  two  cleavages. 
Its   hardness   is   about  3  and   its 
sp.gr.  about  3.9.     Its  luster  and  streak  are  like  those 
of  barite. 

Before  the  blowpipe,  celestite  reacts  like  barite, 
except  that  it  tinges  the  flame  crimson.  It  is  insoluble 
in  water  and  acids. 

Celestite  is  easily  distinguished  from  all  minerals 


DESCRIPTION  OF  MINERALS  63 

but  the  sulphates  by  its  appearance  and  its  reaction 
for  sulphur.  It  is  distinguished  from  the  other  sul- 
phates by  its  sp.gr.  and  the  crimson  color  it  gives  to 
the  flame. 

It  occurs  in  beds  with  rock  salt  (No.  27)  and  gyp- 
sum (No.  67),  in  groups  of  crystals  associated  with 
sulphur  (No.  3),  and  as  isolated  crystals  in  limestone. 
It  is  found  also  in  massive  veins. 

It  is  used  to  some  extent  as  a  source  of  strontium 
compounds. 

65.  Anglesite  (PbSC^)  occurs  principally  as  com- 
plicated   crystals    (Fig.    43),    associated   with   galena 
(No.  9)    and  other  ores  of  lead, . 
but  it  is  found  also  massive  and 
in  granular,  stalactitic  and  globu- 
lar forms.    Its  crystals  are  usually 

rp,   *  FIG.  43.— Anglesite 

prismatic.      They    possess    two  Crystal. 

cleavages. 

The  mineral  is  white,  gray  or  colorless,  and  its  sur- 
faces are  often  tarnished  with  a  gray  coating.  It  is 
transparent  and  brittle,  has  a  white  streak  and  a 
vitreous  or  resinous  luster.  Its  hardness  is  2.5  to  3 
and  its  sp.gr.  6.3. 

When  heated  before  the  blowpipe,  the  mineral 
decrepitates.  It  fuses  in  the  flame  of  a  candle.  If 
heated  on  charcoal  with  the  reducing  flame,  it  effer- 
vesces and  yields  a  globule  of  metallic  lead.  It  also 
readily  gives  the  sulphur  reaction  (p.  146),  It  dis- 
solves in  HNOs  with  difficulty. 

Anglesite  is  characterized  by  its  high  sp.gr.  and  its 
reactions  for  lead  and  sulphur. 

It  is  found  in  crystals  implanted  on  galena  and  other 
lead  minerals  and  sometimes  as  the  filling  of  veins. 


64  MINERALS  AND  ROCKS 

It  is  mined  with  other  minerals  as  an  ore  of  lead. 

66.  Alunite  (K(A1(OH) 2)3(804)2)  usually  occurs  in 
tabular  crystals,  in  compact  and  crystalline  masses 
and  in  aggregates,  composed  of  particles  of  the  mineral 
and    silicious    materials,    forming    a    hard,    granular, 
nearly  white  rock. 

Alunite  is  white,  gray  or  pink,  and  has  a  white 
streak.  It  is  translucent  and  has  a  vitreous  or  por- 
celain-like luster.  Its  hardness  is  3.5^  and  its  sp.gr. 
2.6-2.75. 

Before  the  blowpipe  it  decrepitates  but  is  infusible. 
In  the  closed  tube  it  yields  water.  With  the  proper 
treatment  it  reacts  for  aluminium  (p.  147)  and  sul- 
phur (p.  146).  It  is  soluble  in  hydrochloric  acid. 

If  differs  from  gypsum  (No.  67)  by  its  greater 
hardness  and  from  anhydrite  (No.  62)  by  its  infusibility 
and  the  color  it  imparts  to  the  flame.  From  aragonite 
and  magnesite  (Nos.  56,  52),  it  is  distinguished  by  the 
test  for  CO2  (p.  149),  and  from  chert  (p.  192)  by  its 
inferior  hardness. 

Alunite  is  commonly  found  in  veins  cutting  vol- 
canic rocks.  It  has  been  utilized  as  a  source  of  alum 
and  is  now  being  mined  as  a  source  of  aluminium  and 
potassium.  Massive  varieties  are  used  for  millstones. 

Hydrated  Sulphates 

67.  Gypsum  (CaSO4-2H2O)  is  the  most  important 
of  all  the  sulphates.     It  is  far  more  common  than 
the    corresponding   anhydrous   compound,    anhydrite 
(CaS04),  (No.  62).     It  occurs  in  massive  beds  associ- 
ated with  limestone  and  rock  salt,  in  finely  granular 
aggregates,   in  fibrous   groups,  and  in  crystals.     The 


DESCRIPTION  OF  MINERALS  65 

crystals  are  well-characterized,  monoclinic  forms  (Fig. 
44)  with  a  tabular  habit,  which  are  often  twinned  in 
such  a  way  as  to  produce  swallow-tail  or  arrow-shaped 
pairs. 

The  mineral  is  white,  or  colorless,  and  transparent 
or  translucent  when  pure;  gray,  red,  yellow,  blue  or 
black  when  impure.  It  possesses  one  good  cleavage, 
yielding  thin  inelastic  folise.  The  luster  is  pearly  on 
cleavage  surfaces  and  vitreous  on  all  others.  Massive 


\/ 

FIG.  44. — Gypsum  Crystals. 

varieties  are  dull.  The  mineral  has  a  hardness  of 
only  1.5-2  and  a  sp.gr.  of  2.32. 

In  the  closed  glass  tube,  gypsum  yields  abundant 
water  and  falls  into  a  white  powder  which  reacts  alka- 
line. It  colors  the  blowpipe  flame  yellowish-red  and 
yields  the  sulphur  test  on  a  silver  coin.  It  is  slightly 
soluble  in  water  and  readily  soluble  in  HC1.  When 
heated  to  250°  it  loses  water  and  disintegrates  into 
powder,  which  when  ground  becomes  "  plaster  of 
Paris".  This,  when  moistened  with  water,  again 
combines  with  it  and  crystallizes  into  an  aggregate 
of  interlocking  crystals.  This  process  constitutes  the 
"set." 

Gypsum  is  distinguished  from  other  easily  cleavable, 
colorless  minerals  by  its  softness,  and  the  reaction  for 
sulphur  (p.  146). 


66  MINERALS  AND  ROCKS 

The  varieties  of  gypsum  generally  recognized  are: 
Selenite,  the  transparent,  crystallized  variety. 
Satin  spar,  a  finely  fibrous  variety. 
Alabaster,  a  fine-grained  granular  variety. 
Rock-gypsum,    a   massive,    structureless,    often 

impure  and  colored  variety. 
Gypsite  is  gypsum  mixed  with  earth. 
Gypsum  occurs  in  numerous  beds  interstratified 
with  limestone,  clay  and  halite,  and  as  crystals  em- 
bedded in  limestone,  clay  or  sand,  or  implanted  on 
the  rocks  around  volcanic   vents.     It  is  found  also 
as  gypsite  in  hills  of  wind-blown  sand. 

Crude  gypsum  is  used  in  the  manufacture  of  plaster, 
as  a  retarder  in  Portland  cement,  and  as  a  fertilizer, 
under  the  name  of  land  plaster.  The  calcined  min- 
eral is  used  as  plaster  of  Paris  and  in  the  manu- 
facture of  finishing  plasters,  and  certain  kinds  of 
cements.  Alabaster  is  a  medium  for  sculpture. 

TUNGSTATES,   MOLYBDATES  AND    CHROMATES 

The  tungstates  are  salts  of  tungstic  acid,  H2WO4,* 
the  molybdates,  salts  of  molybdic  acid,  EbMoCX; 
and  the  chromates,  salts  of  chromic  acid,  H2CrO4. 

68.  Scheelite  (CaWO4)  is  one  of  the  most  important 
ores  of  tungsten.  It  occurs  in  granular  and  globular 
masses  and  in  tetragonal  pyramidal  crystals  (Fig.  45). 

The  mineral  is  white,  yellow,  brown,  greenish  or 
reddish,  with  a  white  streak  and  a  vitreous  luster. 
It  has  one  distinct  cleavage  and  an  uneven  break. 
It  is  brittle,  has  a  hardness  of  4.5-5,  and  a  sp.gr.  of 
about  6.  It  is  transparent  or  translucent. 

Before  the  blowpipe,  scheelite  fuses  to  a  semi- 
transparent  glass.  Heated  with  borax  it  forms  a 


DESCRIPTION  OF  MINERALS  67 

transparent  glass,  which  becomes  opaque  on  cooling. 
With  microcosmic  salt  it  gives  the  characteristic 
blue  beads  for  tungsten  (p.  141),  but  specimens 
containing  iron  must  first  be  heated  with  tin  on  char- 
coal before  the  blue  bead  can  be  produced.  It  is 
soluble  in  HC1  and  HNOs  with  the  production  of  a 
yellow  powder  (WOs),  and  solutions  which  give 
the  characteristic  tungsten  reaction  (p.  165). 

Massive  scheelite  is  distinguished  from  limestone 
by  its  higher  sp.gr.  and  the  absence  of  effervescence 
with  HC1.  It  is  distinguished  from  quartz  by  its 


FIG.  45.— Scheelite  Crystals. 

softness  and  from  barite  by  its  greater  hardness, 
and  from  both  by  its  higher  sp.gr. 

The  mineral  is  found  in  veins  associated  with 
topaz,  fluorite,  molybdenite,  wolframite  (Nos.  91,  29,  8, 
69),  and  many  metallic  ores. 

It  is  mined  as  an  ore  of  tungsten,  which  is  used 
principally  in  the  manufacture  of  tool  steel.  The 
metal  is  employed  also  as  filaments  in  incandescent 
lamps  and  in  the  manufacture  of  sodium  tungstate, 
which  is  used  for  fire-proofing  cloth.  Its  salts  are  used 
as  mordants  in  dyeing,  and  for  a  number  of  minor 
purposes. 

69.  Wolframite  ((Fe,Mn)W04)  is  the  name  given 
to  a  series  of  compounds  that  are  mixtures  of  FeWC>4 


68  MINERALS  AND  EOCKS 

and  MnWO4,  which  when  pure  are  known  as  ferberite 
and  huebnerite. 

Wolframite  occurs  in  prismatic  crystals  (Fig.  46), 
which  have  one  perfect  cleavage,  and  in  lamellar  and 
granular  masses. 

Huebnerite  is  black  or  brownish-red  and  trans- 
lucent. Wolframite  is  black  and  translucent  on  very 
thin  edges,  and  ferberite  is  black 
and  opaque.  The  streak  of  hueb- 
nerite is  yellow  or  yellowish-brown; 
of  ferberite,  brown  or  brownish-black; 
and  of  wolframite,  yellowish-brown 
or  brown. 

Before  the  blowpipe,   wolframite 
FIG.  46.  f  i  u  i     A,   ,  • 

Wolframite  Crystal,    fuses  to  a  globule  that  is  magnetic. 

Fused  with  soda  and  niter  on  plat- 
inum, it  gives  a  bluish-green  manganate.  It  dis- 
solves in  aqua-regia  with  the  production  of  the 
yellow  WOs,  and  when  treated  with  H2S04  and  tin 
it  yields  the  blue  tungsten  reaction  (p.  165). 

Wolframite  is  distinguished  from  columbite  (No. 
79),  samarskite  (No.  81)  and  uraninite  (No.  84)  by 
its  more  perfect  cleavage  and  its  reactions  with  the 
beads.  It  is  distinguished  from  black  tourmaline 
(No.  108)  by  the  difference  in  sp.gr. 

The  mineral  usually  occurs  in  veins  with  tin 
ores,  and  as  grains  and  crystals  in  coarse-grained 
granites. 

Wolframite  (including  huebnerite  and  ferberite) 
is  the  most  important  source  of  tungsten. 

70.  Wulfenite  (PbMoCU)  occurs  principally  in 
thin,  tabular  crystals  (Fig,  47)  implanted  on  minerals 
and  the  walls  of  cracks  and  pores  in  veins  of  lead  ores. 


DESCRIPTION  OF  MINERALS  69 

The  mineral  is  orange,  olive,  gray,  brown,  bright 
red  or  colorless.  It  is  brittle  and  transparent.  Its 
streak  is  white,  its  luster  resinous  or  adamantine. 
Its  hardness  is  3,  and  sp.gr.  6.8.  It  has  a  very  smooth 
cleavage  parallel  to  the  faces  of  a 
pyramid.  x  : 

Before    the    blowpipe,    wulfenite 
decrepitates  and  fuses  easily.    Heated    Wulfenite  Crystal, 
with   Na2C03   on   charcoal   it   gives 
lead  globules.     It  gives  also  the  usual  reactions  for 
molybdenum    (p.    160).      It  is  decomposed  on  evap- 
oration with  HC1,  yielding  lead  chloride  and  molybdic 
oxide.     This  when  placed  in  a  little  water  and  treated 
with  zinc  turns  blue. 

Wulfenite  is  distinguished  from  vanadinite  (No. 
75)  by  crystallization,  by  the  test  for  chlorine  (vana- 
dinite), and  the  blue  solution  test  for  molybdenum 
(p.  149). 

The  mineral  is  an  important  source  of  molybdenum. 

71.  Crocoite  (PbCr04)  occurs  in  hyacinth-red 
granular  masses  and  in  small  prismatic  crystals  im- 
planted on  the  walls  of  cracks  in  rocks. 

Its  color  is  usually  bright  red  and  its  streak  orange- 
yellow.  It  is  translucent  and  sectile.  Its  hardness 
is  2.5-3,  and  its  density  about  6. 

In  the  closed  tube  it  decrepitates  and  blackens, 
but  it  reassumes  its  original  color  on  cooling;  on  char- 
coal it  deflagrates  and  fuses  easily,  yielding  a  lead 
globule  and  sublimate.  With  microcosmic  salt  it 
gives  the  green  bead  of  chromium  (p.  141).  The 
mineral  dissolves  in  HC1,  yielding  a  solution  which 
upon  the  addition  of  tin  turns  apple-green,  then 
brownish,  and  finally  red. 


70  MINEEALS  AND  ROCKS 

Crocoite  is   easily   distinguished   from   vanadinite 
(No.  75)  by  the  test  for  chlorine  (p.   154),  and  from 
wulfenite  (No.  70)  by  the  tests  for  molybdenum  (p. 
149)  and  chromium  (p.  141). 
,     Crocoite  has  no  commercial  value. 

PHOSPHATES,  ARSENATES  AND  VANADATES 


The  normal  phosphates  are  salts  of  the  acid 
the  normal  arsenates  of  the  corresponding  H3As04> 
and  the  normal  vanadates  of  H3VO4.  Some  minerals 
are  normal  salts,  but  the  greater  number  are  basic, 
acid  or  double  salts,  and  many  are  hydrated.  The 
most  important  are  the  members  of  the  apatite  group. 

Anhydrous  Phosphates,  Arsenates  and  Vanadates 

APATITE    GROUP 

72.  Apatite  (Ca4(Ca(Cl,F))(PO4)3)  is  the  most  com- 
mon of  all  the  phosphates.  It  occurs  in  crystals,  in 
massive,  granular  and  fibrous  forms  and  in  globular 
masses. 

Its  crystals  are  hexagonal  prisms  or  pyramids,  or  a 
combination   of   the   two    (Fig.   48).     Their  habit   is 
usually  prismatic. 

Apatite  is  colorless,  white,  green 
or  brown,  and  transparent,  or  opaque. 
It  has  a  white  streak,  a  vitreous 

FIG.  48.—  Apatite  - 

Crystals.  luster,  a  hardness  of  4.5-5,  and  a 
sp.gr.  of  3.2. 

Before  the  blowpipe  it  fuses  with  difficulty,  coloring 
the  flame  yellowish-red.  When  moistened  with  EbSO^ 
and  heated,  the  flame  is  tinged  a  bluish  green  (phos- 


DESCRIPTION  OF  MINEEALS  71 

phoric  acid).  Some  specimens  react  for  chlorine  with 
copper  oxide  (p.  154),  others  for  fluorine  (p.  155). 
If  fused  with  a  little  piece  of  magnesium  ribbon  a 
phosphide  is  produced,  which,  when  moistened  with 
water,  gives  the  odor  of  moist  phosphorus.  The 
mineral  dissolves  in  HC1  and  HNOs. 

Apatite  is  easily  recognized  by  its  crystals  and  the 
test  for  phosphorus.     It  is  distinguished  from  beryl 
(No.  103)  by  its  greatly  inferior  hardness,  and  from 
calcite  by  the  fact  that  it  does  not  effervesce  in  acids. 
The  varieties  recognized  by  distinct  names  are : 
Ordinary  apatite,  crystals  or  granular  masses. 
Mangan-apatite,  in  which  Mn  partially  replaces 
the  Ca  of  ordinary  apatite.     This  is  dark 
bluish-green. 

Phosphorite,  fibrous,  concretionary  apatite. 
Phosphate  rock  is  a  mixture  of  apatite,  phos- 
phorite and  various  hydrated  phosphates 
often  mixed  with  bones,  teeth,  etc.  It  is, 
properly,  a  rock  with  a  brecciated  and  con- 
cretionary structure. 

Apatite  occurs  in  igneous  and  sedimentary  rocks, 
in  veins  with  magnetite  and  cassiterite,  and  in  beds 
(phosphate  rocks). 

The  mineral  is  used  principally  in  the  manufacture 
of  fertilizers. 

73.  Pyromorphite  (Pb4(PbCl)(PO4)3)  occurs  prin- 
cipally as  small  crystals  implanted  on  the  walls  of 
cracks  and  cavities  in  rocks,  and  as  globular,  granular 
and  fibrous  masses. 

Its  crystals  are  similar  to  those  of  apatite,  but  are 
often  rounded  on  their  edges  and  sometimes  are 
skeletons  (Fig.  49). 


72  MINEEALS  AND  ROCKS 

Pyromorphite  is  gray,  white,  or  orange,  but  more 
commonly  green,  yellow  or  brown.     Its  streak  is  white, 
its  luster  resinous,  its  hardness  3.5-4, 
and  its  sp.gr.  about  7.     It  is  translu- 
cent and  brittle. 

When  heated  in  the  closed  glass 
tube,  the  mineral  fuses  and  gives  a 
white  sublimate  of  lead  chloride.     It 
colors  the  blowpipe  flame  bluish-green. 
FIG.  49.— Skeleton    When  fused  On  charcoal,  it  melts  to 

Crystal  of  . 

Pyromorphite.  a  globule  which  crystallizes  on  cooling 
and  yields  a  coating  which  is  yellow 
(PbO)  near  the  assay,  and  white  (PbCl2)  at  a 
distance  from  it.  It  yields  also  the  other  reactions 
for  lead  (p.  158),  and  those  for  chlorine  (p.  154) 
and  phosphorus  (p.  161).  The  mineral  is  soluble  in 
acids. 

Pyromorphite  is  easily  recognized  by  its  forms,  high 
sp.gr.  and  its  action  when  heated  on  charcoal. 

It  occurs  principally  in  veins  with  other  lead  ores. 

It  possesses  no  commercial  value,  except  as  it  is 
mined  with  other  minerals  as  an  ore  of  lead. 

74.  Mimetite  (Pb4(PbCl)(As04)3)  is  very  much 
like  pyromorphite  in  appearance  and  manner  of 
occurrence,  and  in  most  of  its  properties.  It  is  usually, 
however,  a  little  lighter  in  color  and  its  sp.gr.  is  a 
little  greater  (7-7.2). 

It  fuses  more  easily  than  pyromorphite  (No.  73), 
and  when  heated  on  charcoal  it  yields  arsenical  fumes. 
This  distinguishes  it  from  the  phosphate. 

The  mineral  is  not  as  common  as  pyromorphite. 
It  occurs  in  veins  with  other  lead  minerals  and  is  mined 
with  them  as  an  ore  of  lead. 


DESCRIPTION  OF  MINERALS  73 

75.  Vanadinite  (Pb4(PbCl)(V04)3)  is  easily  recog- 
nked  by  its  bright  red  prismatic  crystals  (Fig.   50), 
implanted  on  the  walls  of  cracks  and  crevices  in  rocks 
or  on  the  surfaces  of  other  minerals.     It 
occurs   also    in   globular   masses   and   in 
crusts. 

Its  crystals  are  usually  small  hexagonal 
prisms  that  show  hollow  faces.  Often 
they  are  grouped  in  little  pyramids. 

Vanadinite  is  brittle.     It  has  a  hard-     vanadfnite 
ness  of  about  3  and  a  sp.gr.  of  about  7.       Crystal. 
Its  luster  is  resinous,  and  its  color  ruby- 
red,    brownish-yellow    or   reddish-brown.     Its  streak 
is  white  or  yellow.     It  is  translucent  or  opaque. 

Heated  in  the  closed  glass  tube,  vanadinite  decrepi- 
tates; on  charcoal  it  fuses  easily  to  a  black  lustrous 
mass  which,  upon  further  heating  in  the  reducing  flame, 
yields  globules  of  lead  and  a  white  sublimate  of  PbCh. 
After  complete  oxidation  of  the  lead  by  heating  with 
the  oxidizing  flame  on  charcoal,  the  residue  gives  an 
emerald-green  bead  in  the  reducing  flame  with  micro- 
cosmic  salt  (p.  141).  The  mineral  also  gives  the  test 
for  chlorine  (p.  154).  It  is  soluble  in  HC1.  The  addi- 
tion of  metallic  tin  to  this  solution  will  cause  it  to  turn 
blue  (p.  166)  in  consequence  of  the  reduction  of  the 
vanadium  compounds  by  nascent  hydrogen.  Some 
specimens  also  give  the  test  for  arsenic  (p.  151). 
When  vanadium  and  arsenic  are  present  in  nearly 
equal  quantities,  the  substance  is  known  as  end- 
lichite. 

Vanadinite  is  easily  distinguished  from  most  other 
minerals  by  its  color.  It  is  distinguished  from  wulfen- 
ite  (No.  70)  by  the  shape  of  its  crystals  and  the  reac- 


74  MINERALS  AND  ROCKS 

tions  for  chlorine  and  vanadium;  and  from  crocoite 
(No.  71)  by  the  tests  for  chromium  and  chlorine. 

The  mineral  occurs  principally  in  regions  of  volcanic 
rocks. 

It  is  an  important  source  of  vanadium,  which  is 
employed  in  the  manufacture  of  certain  grades  of  steel 
and  bronze.  Its  compounds  are  used  as  pigments  and 
mordants. 

Hydrated  Phosphates  and  Ar senates 

76.  Wavellite  ((A1(OH,F))3(PO4)2-5H2O)  is  one  of 
the  commonest  of  hydrated  phosphates.  It  rarely 


FIG.  51. — Radiating  Groups  of  Wavellite  Crystals  on  a  Rock  Surface. 

occurs  in  crystals.     It  is  usually  in  globular  or  radiating 
groups  of  fibers  (Fig.  51). 

The  mineral  is  vitreous  in  luster,  translucent  and 
white,  green,  yellow,  brown  or  black.  Its  streak  is 
white.  It  is  brittle,  infusible  and  insoluble.  Its 
hardness  is  3.5  and  density  2.3. 


DESCRIPTION  OF  MINERALS  75 

Heated  in  a  closed  -glass  tube,  wavellite  yields 
water,  the  last  traces  of  which  react  acid  and  often 
etch  glass  (HF).  In  the  blowpipe  flame  it  swells  and 
breaks  into  tiny  infusible  fragments,  at  the  same  time 
tinging  the  flame  green.  It  is  soluble  in  HC1  and 
H^SCU.  When  heated  with  IbSCU  many  specimens 
yield  HF,  which  etches  glass.  If  heated,  moistened 
with  Co(NOs)2  solution  and  again  heated,  the  mineral 
turns  blue. 

Wavellite  is  distinguished  from  turquoise  (No.  78) 
by  its  action  in  the  blowpipe  flame,  by  its  inferior 
hardness  and  its  manner  of  occurrence. 

The  mineral  is  usually  found  as  radiating  bundles  of 
fibers  on  the  walls  of  cracks  in  rocks  and  as  globular 
masses  filling  their  pores  and  larger  cavities. 

It  has  no  economic  value. 

77.  Erythrite  (Co3(AsO4)2-8H2O)  is  not  a  common 
mineral,  but  it  is  included  here  because,  being  an  alter- 
ation product  of  other  cobalt  compounds,  it  is  an 
important  indicator  of  the  presence  of  cobalt  ore.  It 
is  easily  recognized  by  its  rose-red  color. 

It  usually  occurs  in  slender  prismatic~crystals 
arranged  in  divergent  and  irregular  groups,  in  crusts, 
or  in  earthy  masses.  It  possesses  one  perfect  cleavage. 

It  is  transparent  or  translucent;  has  a  gray,  crim- 
son, rose-red  or  peach-red  color  and  a  white  or  pink 
streak.  Its  hardness  varies  between  1.5  and  2.5,  and 
its  sp.gr.  is  2.95.  Its  luster  is  pearly  on  cleavage  planes 
and  vitreous  on  other  surfaces.  It  is  flexible  and  sectile. 

Heated  in  the  closed  glass  tube,  erythrite  turns 
blue  and  yields  water  at  a  low  temperature.  At  a 
high  temperature  it  produces  a  dark  sublimate.  In 
the  blowpipe  flame  it  fuses  easily  and  tinges  the  flame 


76  MINERALS  AND  ROCKS 

pale  blue.  On  charcoal  it  fuses  and  yields  arsenic 
fumes  and  a  gray  globule  which  colors  the  borax  bead 
deep  blue  (p.  141).  It  is  soluble  in  HC1,  producing 
a  pink  solution,  which  upon  evaporation  to  dryness 
gives  a  blue  stain. 

Erythrite  is  easily  recognized  by  its  color  and  cobalt 
reactions.  From  pink  tourmaline  (No.  108)  it  is 
distinguished  by  hardness  and  easy  fusibility. 

The  mineral  is  found  principally  in  veins  of  cobalt 
ores,  more  particularly  near  the  surface,  where  it 
sometimes  occupies  the  entire  width  of  the  veins. 

It  usually  accompanies  other  cobalt  minerals  in 
small  quantity  and  is  mined  with  them  as  an  ore  of 
cobalt.  Its  principal  importance  arises  from  the  fact 
that  it  is  a  surface  indication  of  the  presence  beneath 
of  more  important  cobalt  ores. 

78.  Turquoise  (6(A1(OH)2)  -CuOH-HsCPO^)  may 
be  an  acid  phosphate,  that  is,  a  phosphate  in  which 
some  of  the  H  of  the  acid  has  not  been  replaced  by 
bases.  It  is  more  likely,  however,  a  mixture  of 
(A1(OH)2)2HP04  and  (CuOH)2HP04. 

Crystals  are  extremely  rare.  As  usually  found,  the 
mineral  is  an  amorphous  or  cryptocrystalline  trans- 
lucent material  with  a  waxy  luster  and  a  sky-blue, 
green  or  greenish-gray  color,  and  a  white  streak.  Its 
fracture  is  conchoidal,  its  hardness  6,  and  its  sp.gr. 
2.7.  It  is  brittle. 

In  the  closed  glass  tube  it  decrepitates,  yields  water, 
and  turns  black  or  brown.  It  is  infusible,  but  it  as- 
sumes a  glassy  appearance  when  heated,  and  colors 
the  flame  green.  When  moistened  with  HC1  and  again 
heated  the  flame  is  tinged  with  the  azure  blue  of  copper 
chloride.  The  mineral  is  soluble  in  HC1. 


DESCRIPTION  OF  MINERALS  77 

Turquoise  is  usually  easily  recognized  by  its  color, 
its  hardness  and  its  reactions  for  water  and  copper. 

It  is  found  in  narrow  veins  and  irregular  masses  in 
certain  brecciated  volcanic  rocks. 

It  is  an  important  gem  stone.  Small  pieces  of  rock 
containing  tiny  veins  of  the  mineral  are  polished  and 
used  under  the  name  turquoise  matrix. 

COLUMBATES   AND    TANTALATES 

The  commonest  columbates  and  tantalates  are 
salts  of  the  meta  acids  H2Cb2O6  and  H2Ta2O6,  the 
relations  of  which  to  the  normal  acids  are  indicated  by 
the  equation :  2H3Cb04  -  2H20  =  H2Cb206. 

79.  Columbite  ((Fe,Mn)Cb2O6)  and  (80.)  Tantalite 
((Fe,Mn)Ta2O6)  are  the  names  given  to  the  nearly 


FIG.  52.— Columbite  Crystals. 

pure  columbates  and  tantalates  of  iron  and  manganese. 
So  rarely,  however,  are  these  compounds  found  pure 
that  the  name  columbite  usually  refers  to  their 
mixtures. 

Columbites  occur  mainly  in  short  prismatic  crys- 
tals (Fig.  52)  in  coarse  granite  dikes. 

The  minerals  are  usually  opaque,  black  and  lustrous, 
though  occasionally  brown  and  translucent.  Their 
streak  is  black  or  brown.  They  possess  one  distinct 


78  MINERALS  AND  EOCKS 

cleavage.  Their  hardness  is  6,  and  sp.gr.  between 
5.3  and  7.3,  increasing  with  the  proportion  of  Ta 
present. 

The  minerals  are  not  affected  by  the  blowpipe. 
When  columbite  is  decomposed  by  fusion  with  KOH 
and  the  result  of  the  fusion  is  dissolved  in  HC1  and 
H2S04  this  solution  turns  blue  on  the  addition  of 
metallic  zinc.  The  mineral  is  also  partially  decom- 
posed when  evaporated  to  dryness  with  H2SO4,  forming 
a  white  compound  that  changes  to  yellow.  This 
residue  boiled  with  HC1  and  zinc  turns  blue.  Tantal- 
ite  is  decomposed  by  fusion  with  KHSCU  on  platinum. 
This,  when  heated  with  dilute  HC1  yields  a  yellow 
solution  and  a  heavy  white  powder.  Upon  the  addi- 
tion of  zinc  the  powder  becomes  blue.  The  color 
disappears  on  the  addition  of  more  water. 

Columbite  may  easily  be  confused  with  black  tour- 
maline (No.  108),  ilmenite  (No.  132),  and  wolframite 
(No.  69).  From  tourmaline  it  is  distinguished  by 
crystallization,  by  high  sp.gr.  and  luster;  from  wolfram- 
ite by  less  perfect  cleavage  and  the  reaction  with  aqua- 
regia  and  from  ilmenite  by  the  test  for  titanium 
(p.  164). 

Tantalite  has  a  slight  value  as  a  source  of  tantalum, 
which  is  used  for  filaments  in  certain  types  of  incan- 
descent lamps.  Columbite  has  no  value. 

81.  Samarskite  and  (82.)  Yttrotantalite  are  com- 
plicated mixtures  of  yttrium,  erbium,  cerium,  thorium 
and  other  salts  of  pyrocolumbic  and  pyrotantalic 
acids  (H4Cb2O7  and  H4Ta207)  which  are  related  to 
the  normal  acids  as  follows:  2HsCb04  —  H2O  = 
H4Cb207.  The  compound  in  which  the  columbates 
predominate  is  samarskite;  that  in  which  the  tanta- 


DESCRIPTION  OF  MINERALS  79 

lates  are  in  excess  is  yttrotantalite.     They  can  be 
distinguished  from  one  another  only  by  analysis. 

The  minerals  are  usually  massive,  but  occasionally 
they  occur  in  prismatic  crystals  (Fig.  53).  Samarskite 
is  velvety  black,  opaque  and  brittle.  Its  streak  is 
reddish-brown,  its  hardness  5  to  6,  and  its  sp.gr.  5.7. 
Yttrotantalite  is  black,  brown  or  yellow.  Its  luster 
is  submetallic  or  vitreous;  its  streak  gray  to  colorless; 
its  hardness  5-5.5;  and  its  sp.gr. 
5.5-5.9.  Some  specimens  are  opaque 
and  others  translucent. 

The  reactions  of  both  minerals 
are  extremely  complex  because  of  the 
great  number  of  elements  usually 
present  in  them.  They  always  yield, 
however,  the  blue-solution  test  for  FlG'  5c~ftaaTsarskite 
columbium  (p.  155)  or  tantalum 
(p.  163),  and  most  specimens  react  for  Mn,  Fe,  Ti 
and  U.  The  test  for  U  is  an  emerald-green  bead 
with  microcosmic  salt  in  both  oxidizing  and  reducing 
flames.  Both  minerals  affect  the  photographic  plate. 

The  two  minerals  are  distinguished  from  wolfram- 
ite, columbite,  and  tantalite  (Nos.  69,  79,  80)  by  the 
forms  of  their  crystals  and  by  the  lack  of  a  distinct 
cleavage.  Samarskite  is  easily  recognized  by  its 
velvety  black  luster. 

Both  minerals  occur  in  coarse  granite  veins. 

Neither  mineral  is  at  present  of  any  commercial 
value.  Both  are,  however,  extremely  interesting  as 
the  sources  of  many  of  the  rare  elements;  and,  especi- 
ally, as  a  possible  source  of  radium. 


80  MINERALS  AND  ROCKS 

URANYL    COMPOUNDS 

The  most  important  compounds  of  uranium  con- 
tain this  element  in  the  form  of  the  radical  uranyl 
(UO2) .  They  are  very  complex  in  composition  and  are 
of  great  interest  because  of  their  content  of  uranium, 
an  element  which  appears  to  be  genetically  related  to 
radium.  The  two  prominent  sources  of  uranium  and 
radium  are  the  vanadate,  carnotite,  and  the  uranate, 
uraninite. 

83.  Carnotite  ((Ca,K2)(UO2)2(VO4)2-H20)  is  so 
complex  that  the  formula  given  is  merely  suggestive. 
It  appears  to  be  a  mixture  of  several  vanadates  in 
which  the  potassium  uranyl  vanadate  is  most  promi- 
nent. Many  specimens  contain  also  As,  P,  Si,  Ti,  Mo, 
Fe,  Al,  Pb,  Cu,  Ca,  Ba,  K  and  other  elements. 

The  mineral  has  been  found  in  tiny  yellow  crys- 
talline grains  and  powder  in  the  interstices  between 
the  grains  of  sandstones  and  conglomerates,  and  as 
nodules  and  lumps  in  these  rocks.  With  a  decrease  in 
the  proportion  of  U  present  its  color  becomes  duller, 
and  with  increase  in  vanadium  it  gradually  changes 
to  olive-green  and  finally  to  brick-red.  The  color  of 
the  streak  is  paler  than  that  of  the  mineral. 

At  a  moderate  heat  carnotite  becomes  black  and 
melts.  With  microcosmic  salt  and  a  little  Na2COs 
it  fuses  to  a  clear  glass,  which  when  cold  is  bright  green. 
The  mineral  is  soluble  in  HNOs.  If  to  the  solution 
hydrogen  peroxide  be  added,  it  will  become  brown. 
Moreover,  the  mineral  yields  all  the  reactions  for 
vanadium  (p.  166).  It  is  radioactive. 

Carnotite  is  one  of  the  main  sources  of  radium  and 
uranium  and  is  one  of  the  sources  of  vanadium.  Al- 


DESCRIPTION  OF  MINERALS  81 

though  it  contains  a  notable  quantity  of  uranium,  it  has 
little  value  as  an  ore  of  this  metal,  because  of  the  few 
uses  to  which  uranium  is  put.  This  metal  is  used  to 
some  extent  in  making  steel  alloys  and  in  the  manu- 
facture of  iridescent  glazes  and  glass.  Its  compounds 
are  used  in  certain  chemical  determinations  and  as 
medicines,  in  photography,  as  porcelain  paint,  and  as 
a  dye  in  calico  printing.  The  uses  of  vanadium  have 
been  referred  to  elsewhere  (p.  74).  Radium,  because 
of  its  scarcity  and  its  possible  value  as  a  therapeutic 
agent,  has  a  selling  price  of  about  $2,000,000  per 
ounce  in  the  form  of  the  chloride.  As  the  quantity 
of  this  element  present  varies  with  the  quantity  of 
uranium,  the  price  of  the  ore  is  based  on  its  percentage 
of  UsOg.  Carnotite  containing  2  per  cent.  U308  and 
5  per  cent.  V205  was  quoted  in  1913  at  $1.25  per 
pound. 

84.  Uraninite  or  pitchblende  (UaOs)  is  the  only 
important  source  of  radium  besides  carnotite.  It  is 
an  extremely  complicated  mixture  of  UO2,  UO3, 
Th02  and  PbO  with  small  quantities  of  ZrC>2,  CeC>2, 
La203,  Di203,  Y2O3,  Er203,  MnO,  CuO,  and  many 
other  oxides,  besides  helium,  argon  and  radium.  It 
may  be  regarded  as  a  uranyl-uranate,  (UO2)2UO4, 
in  which  Pb,  Th  and  other  basic  elements  replace  a 
part  of  the  U02. 

Uraninite  is  found  in  cubic  crystals  and  in  crystal- 
line and  botryoidal  masses.  Crystals  are  rare. 

The  mineral  is  gray,  brown  or  black  and  opaque. 
Its  streak  is  brownish-black,  gray  or  olive-green  and 
its  luster  pitch-like  or  dull.  Its  fracture  is  conchoidal; 
its  hardness  5.5;  and  its  sp.gr.  9  to  9.7.  It  is  brittle. 
Like  other  uranium  compounds,  it  is  radioactive. 


82  MINERALS  AND  ROCKS 

Before  the  blowpipe  it  is  infusible.  Some  speci- 
mens color  the  flame  green  (Cu).  With  borax  it  gives 
a  yellow  bead  in  the  oxidizing  flame,  turning  green  in 
the  reducing  flame.  All  specimens  give  reactions  for 
lead  and  many  for  S  and  As.  Uraninite  is  soluble  in 
HN03  and  H2S04  with  slight  evolution  of  helium,  the 
ease  of  solubility  increasing  with  increase  in  the  pro- 
portion of  rare  earths  present.  If  roasted,  mixed  with 
Na2CC>3  and  KNOs  and  fused,  and  then  treated  with 
HC1,  a  yellow  powder  will  be  produced  after  a  few 
minutes,  and  this  will  change  to  scarlet  on  being 
heated. 

Uraninite  is  distinguished  from  wolframite  (No.  69), 
columbite  (No.  79)  and  tantalite  (No.  80)  by  lack  of 
cleavage,  and  from  these  minerals  and  samarskite  (No. 
81)  by  its  greater  sp.gr.  and  by  differences  in  crystal- 
lization. 

Uraninite  occurs  in  coarse  granite  dikes,  and  in 
veins  with  ores  of  silver,  lead,  copper  and  other  metals. 
It  is  mined  as  a  source  of  uranium  and  radium.  Its 
uses  are  described  in  the  section  on  carnotite  (No.  83). 

SILICATES 

The  silicates  are  salts  of  the  various  silicon  acids, 
H4SiO4,  H2Si03,  H2Si2O5,  H4Si3O8,  etc.  They  include 
the  most  common  minerals  and  those  that  occur  in 
greatest  quantity.  They  make  up  the  greater  portion 
of  the  earth's  crust,  forming  most  of  the  rocks  and  a 
large  portion  of  the  vein  fillings.  In  number  they 
exceed  all  other  minerals,  but  because  of  their  stability, 
only  a  few  are  of  any  commercial  importance,  except 
in  the  form  of  their  aggregates,  the  siliceous  rocks, 
and  as  the  sources  of  their  disintegration  products. 


DESCRIPTION  OF  MINERALS  83 

As  in  the  case  of  other  compounds,  there  are  silicates 
that  contain  H  and  O  in  such  relations  to  their  other 
components  that,  when  heated,  they  yield  water.  In 
some  cases,  this  water  is  given  off  at  a  comparatively 
low  temperature  and  the  compound  is  called  a  hydrate, 
or  is  said  to  contain  water  of  crystallization.  In 
other  cases,  the  water  is  formed  only  at  a  high  tem- 
perature. In  these  instances,  it  is  said  to  be  combined 
and  the  compound  is  usually  basic. 

Anhydrous  Silicates 

85.  Olivine  ((Mg,Fe)2SiO4)  is  the  name  of  mixtures 
of  Mg2Si04  and  Fe2SiO4,  which  occur  nearly  pure 
under  the  names  for  sterile  and  fayalite.  Only  the 
mixture,  olivine,  is  common. 

This  occurs  in  small  prismatic  crystals  and  grains 
and  in  granular  aggregates,  mainly  in  igneous  rocks. 

It  is  yellowish-green,  glassy  and  transparent.  Its 
streak  is  white,  its  cleavage  distinct  in  one  direction, 
its  hardness  between  6.5  and  7,  and  its  sp.gr.  3.27- 
3.37.  The  sp.gr.  of  forsterite  is  about  3.25  and  of 
fayalite,  4.1. 

Before  the  blowpipe  olivine  whitens  but  does  not 
fuse,  except  in  the  case  of  varieties  rich  in  iron.  These 
fuse  to  a  magnetic  globule.  All  the  olivines'are  decom- 
posed by  strong  HC1  and  H2SO4  with  the  separation 
of  gelatinous  silica. 

Olivine  is  easily  recognized  by  its  luster,  its  color 
and  its  solubility  in  acids. 

It  occurs  as  an  original  constituent  of  basic  igneous 
rocks  and  as  a  metamorphic  product  in  dolomitic  lime- 
stones. It  is  also  present  as  rounded  grains  in  some 
meteorites. 


84  MINERALS  AND  ROCKS 

Olivine  alters  easily  to  a  mixture  of  iron  oxides  and 
fibrous  or  scaly  gray  or  green  serpentine  (No.  104), 
according  to  the  reaction,  2Mg2Si04+2H20+C02 
=  H4Mg3Si209+MgC03. 

The  only  member  of  the  group  that  is  of  any  eco- 
nomic importance  is  a  pale,  yellowish-green,  trans- 
parent olivine,  which  is  used  as  a  gem  under  the 
name  peridot. 

86.  Willemite  (Zn2Si04)  is  an  important  ore  of  zinc 
at  a  few  places.      It  occurs  in  prismatic  hexagonal 
crystals  (Fig.  54),  in  grains,  and  massive. 

Nearly  all  willemite  contains  some  man- 
ganese. When  this  is  in  notable  quantity 
(5-7  per  cent  of  MnO)  the  variety  is  known 
as  Troostite  (87.). 

Willemite  is  colorless,  yellow,  brown,  blue 
FIG.  54.  or  black,  while  troostite  is  green,  yellow, 
&raY  or  brown.  Colored  varieties  are  trans- 
lucent, but  colorless  willemite  is  transparent. 
Both  are  vitreous.  Their  hardness  is  between  5  and  6, 
and  their  sp.gr.  between  3.9  and  4.3. 

Both  minerals  glow  when  heated  before  the  blow- 
pipe, and  fuse  with  difficulty.  Both  gelatinize  with 
HC1.  Willemite  reacts  for  Zn  with  Co(N03)2  on  char- 
coal (p.  147)  and  troostite  gives  in  addition  the  reac- 
tions for  Mn  (p.  159). 

Willemite  and  troostite  are  easily  recognized  by 
their  crystals  and  the  reactions  for  zinc  and  manganese. 
Willemite  occurs  in  veins  with  other  zinc  com- 
pounds, but  in  small  quantities  only,  except  at  Frank- 
lin Furnace,  N.  J.,  where  it  occurs  with  troostite  in 
large  quantities,  associated  with  franklinite  (No.  49) 
and  the  zinc  oxide,  zincite  (No.  36). 


DESCRIPTION  OF  MINERALS 


85 


Both  are  mined  with  the  last-named  mineral  as  an 
ore  of  zinc. 

88.  Garnet  (R"3B/"2(Si04)3)  is  the  name  given  to  a 
series  of  compounds  of  the  general  formula  indicated. 
In  this,  R"  =  Ca,  Mg,  Fe  and  R'"=A1,  Fe,  Cr.  Cer- 
tain of  the  compounds  have  been  given  names  of  which 
the  following  are  the  most  common : 

Grossularite  or  Hessonite    Ca3Al2(Si04)3        White,  cinnamon,  pale 

green  or  red 

Mg3Al2(Si04)3       Deep  red  or  black 
Mn3Al2(Si04)3       Yellow,  brownish-red 
Fe3Al2(Si04)3        Red,  brown  or  black 
Ca3Fe2(Si04)3        Black,    brown,    green 

or  yellow 
CasCr2(Si04)3        Emerald  green 


Pyrope 
Spessartite 
Almandite 
Andradite  or  Melanite 

Uvarowite 


Garnets  nearly  always  occur  in  isometric  crystals 
(Fig.   55)    or  in  round   grains.     They  vary  in   color 


FIG.  55.— Garnet  Crystals. 

according  to  composition  (see  above),  the  commonest 
color  being  reddish-brown.  Their  luster  is  vitreous; 
streak,  white;  hardness,  6-7.5;  and  sp.gr.,  3.4-4.3. 
They  are  translucent  or  transparent. 

All,  except  uvarowite,  fuse  fairly  easily  to  a  brown 
or  black  glass  or  globule,  which  in  the  case  of  almandite 
and  melanite  is  magnetic.  Uvarowite  is  infusible. 
Some  garnets  are  unattacked  by  acids;  others  are 


86  MINERALS  AND  ROCKS 

partially  decomposed.  After  ignition,  all  but  uvaro- 
wite  are  decomposed  by  HC1,  with  the  separation  of 
gelatinous  silica  in  most  cases. 

When  in  crystals,  garnets  are  easily  distinguished 
from  most  other  minerals  by  their  forms,  color  and 
hardness.  White  garnets  are  distinguished  from  leu- 
cite  (No.  101)  and  from  analcite  (No.  130)  by  their 
greater  hardness  and  their  insolubility  in  acids.  Mass- 
ive garnet  may  resemble  vesuvianite  (No.  109),  zircon 
(No.  89),  sphene  (No.  131)  or  tourmaline  (No.  108). 
It  is  distinguished  from  zircon  by  its  inferior  hard- 
ness, from  tourmaline  by  its  higher  sp.gr.,  from  sphene 
by  the  reaction  for  Ti,  and  from  vesuvianite  by  its 
lower  sp.gr. 

When  exposed  to  the  atmosphere,  garnets  may  be 
partially  or  entirely  changed  to  epidote  (No.  92), 
muscovite  (No.  96),  chlorites  (No.  100)  or  serpentine 
(No.  104),  and,  consequently,  their  surfaces  may  be 
covered  with  films  of  these  substances,  which  will 
hide  their  true  color  and  hardness. 

Garnets  occur  in  all  rocks  and  in  many  quartz  and 
ore  veins. 

The  varieties  that  are  transparent  are  used  as 
gems,  especially  pyrope,  almandite  and  grossularite. 
Others  are  crushed  and  employed  as  abrasives. 

89.  Zircon  (ZrSiO4)  is  nearly  always  in  crystals 
(Fig.  56),  though  it  is  known  also  in  granular  masses, 
in  irregular  lumps  and  as  rolled  pebbles.  Its  crystals 
are  usually  square  prisms  terminated  by  four-sided 
pyramids. 

It  is  commomy  colored  brown,  reddish,  gray  or 
yellow,  but  in  rare  cases  is  colorless.  Its  streak  is 
always  white.  It  is  transparent  or  translucent  and 


DESCRIPTION  OF  MINERALS 


87 


sometimes  opaque.     Its  luster  is  glossy,  its  hardness 
7.5  and  sp.gr.  4.7. 

Before  the  blowpipe,  it  loses  color,  but  is  infusible 
and   frequently   becomes  white.     It 
is  insoluble  in  acids  and  alkalies. 

It  is  distinguished  by  its  crystal- 
lization, hardness  and  infusibility. 

Zircon  is  a  frequent  constituent 
of  rocks,  of  veins  and  of  river  de- 
posits. 

The  mineral  is  used  as  a  source  of 
zirconia,  which  is  employed  in  incandescent  lamps; 
and  red  and  brown  transparent  varieties  are  utilized 
as  gems  under  the  name  of  hyacinth. 

90.  Andalusite  (Al(A10)SiO4)  is  a  characteristic 
metamorphic  mineral.  It  occurs  principally  as  a 
component  of  shales  that  have  been  intruded  by 


FIG.  56.— Zircon 
Crystals. 


FIG.  57. — Andalusite  Crystals. 


igneous  rocks.  It  is  found  in  crystals  and  in  massive 
and  granular  forms. 

Crystals  are  usually  simple  and  columnar  in 
habit  (Fig.  57)  and  they  possess  good  cleavages  in 
two  directions. 

Andalusite,  when  fresh,  is  greenish  or  reddish  and 
transparent.  Usually,  however,  it  is  more  or  less 
altered,  and  is  opaque,  or  perhaps  translucent,  and 


88 


MINEEALS  AND  EOCKS 


gray,  pink,  or  violet.  The  hardness  of  the  fresh 
mineral  is  7  and  its  sp.gr.  3.2. 

Some  specimens  contain  inclusions  of  a  dark  gray 
or  black,  possibly  carbonaceous,  material  arranged 
in  such  a  way  as  to  form  a  dark  cross,  when  the  crys- 
tals are  cut  across  and  polished.  This  variety  is 
called  chiastolite.  It  was  once  valued  as  a  sacred 
charm. 

Before  the  blowpipe,  andalusite  is  infusible. 
When  moistened  with  cobalt  nitrate  and  heated,  it 
becomes  blue  (see  p.  147).  It  is  insoluble  in  acids. 

Andalusite  is  distinguished  by  its  hardness,  infus- 
ibility,  and  the  reaction  for  Al.  It  is  distinguished 
from  staurolite  (No.  93)  by  the  form  of  its  crystals, 
which  have  a  nearly  square  cross-section. 

The  only  use  of  andalusite  is  as  a  semi-precious 
stone,  and  for  this  purpose  only  the  chiastolite  variety 
is  of  any  value. 

91.  Topaz  (Al(Al(F,OH)2)Si04)  is  a  common  con- 
stituent of  many  ore  veins,  and  is  often  present 


FIG.  58.— Topaz  Crystals. 

as  crystals  on  the  walls  of  cracks  and  cavities  in 
volcanic  rocks.  It  varies  in  composition,  since 
it  is  apparently  a  mixture  of  Al(AlF2)Si04  and 
Al(Al(OH)2)Si04.  It  occurs  massive  and  in  pris- 
matic orthorhombic  crystals  (Fig.  58),  often  contain- 


DESCRIPTION  OF  MINERALS  89 

ing  a  great  number  of  planes.     The  cleavage  is  per- 
fect perpendicular  to  the  long  axes  of  the  crystals. 

The  mineral  is  colorless,  honey-yellow,  yellowish- 
red,  rose  and,  rarely,  bluish.  When  exposed  to  the 
sunlight,  the  colored  varieties  fade,  and,  when  in- 
tensely heated,  some  honey-yellow  crystals  turn  rose- 
red.  The  mineral  is  transparent  and  has  a  colorless 
streak.  Its  hardness  is  8  and  its  sp.gr.  3.5. 

Topaz  is  infusible  before  the  blowpipe  and  in- 
soluble in  acids.  At  a  high  temperature,  it  loses  its 
F  and  OH.  It  gives  the  ordinary  reactions  for  these 
substances. 

The  mineral  is  easily  recognized  by  its  crystalliza- 
tion, its  hardness,  and  its  reaction  for  fluorine  (p.  155). 
It  is  distinguished  from  yellow  quartz  by  its  easy 
cleavage  and  its  greater  hardness. 

It  is  frequently  found  coated  with  a  micaceous 
product  which  may  be  steatite,  muscovite,  or  kaolin 
(Nos.  105,  96,  106). 

Topaz  occurs  principally  in   coarse  granites,  espe- 
cially those  containing  cassiterite  (No.  40),  in  gneisses 
and  in  volcanic  rocks. 
It  is  used  as  a  gem. 

92.  Epidote  (Ca2(Al,Fe)3(OH)(Si04)3)  is  a  common 
alteration  product  of  many  other  silicates.  It  usually 
occurs  in  slender  prismatic  crystals  (Fig.  59),  in  gran- 
ular aggregates  and  massive.  Its  crystals  are  striated 
longitudinally  and  have  one  perfect  cleavage,  which 
in  most  crystals  is  parallel  to  their  long  direction. 

Ordinary  epidote  is  yellowish-green,  dark  green, 
brown,  and  in  some  cases,  red.  It  is  transparent  or 
translucent  and  has  a  glassy  luster  and  a  gray  streak. 
Its  hardness  is  6.5  and  its  density  3.4. 


90  MINERALS  AND  BOOKS 

Two  varieties  that  have  been  given  distinct  names 
are: 

Bucklandite,  a  greenish-black  variety. 

Withamite,  a  bright  red  variety,  containing  Mn. 

Before   the   blowpipe,    epidote   yields   water   and 

fuses  to  a  dark  brown  or  black  mass  which  is  often 

magnetic.     With    increase    in    iron,    fusion    becomes 

easier.     Before    fusion,    the    mineral    is    insoluble   in 


FIG.  59. — Epidote  Crystals. 

acid;  but  after  heating,  it  decomposes  in  HC1  with 
the  separation  of  gelatinous  silica. 

The  ordinary  forms  of  the  mineral  are  characterized 
by  their  yellowish-green  color,  easy  fusibility  and  their 
crystallization.  They  are  distinguished  from  mala- 
chite and  olivine  (Nos.  60,  85)  by  their  insolubility  in 
acids. 

Epidote  occurs  in  veins  and  as  isolated  crystals  and 
druses  on  the  walls  of  fissures  and  cavities  in  rocks. 

It  has  no  economic  value.  Its  presence  is  an 
indication  that  the  rock  in  which  it  occurs  has  been 
subjected  to  weathering  or  other  alteration  processes. 

93.  Staurolite  (Fe(Al-OH)(A10)4(Si04)2)  is  interest- 
ing mainly  because  of  its  cross-shaped  crystals  and  the 
fact  that  it  is  a  characteristic  product  of  metamor- 
phic  processes.  It  crystallizes  in  orthorhombic  pris- 


DESCRIPTION  OF  MINERALS 


91 


matic  crystals  that  are  often  in  twins,  consisting  of 
crossed  crystals  (Fig.  60). 

The  mineral  is  reddish  or  blackish-brown,  with  a 
greasy  luster  and  a  white  streak.  It  is  translucent 
in  fresh  specimens  but  opaque  in  weathered  ones.  It 
possesses  one  distinct  cleavage.  Its  fracture  is  con- 
choidal;  its  hardness  7  and  sp.gr.  about  3.5. 


FIG.  60. — Staurolite  Crystals. 

Before  the  blowpipe,  it  is  infusible,  unless  it  con- 
tains some  manganese,  in  which  case  it  fuses  to  a 
black  magnetic  glass.  It  is  only  slightly  attacked 
by  H2SO4. 

Staurolite  is  easily  recognized  by  its  crystallization, 
infusibility  and  hardness. 

It  occurs  principally  as  crystals  embedded  in 
mica  schists  and  other  metamorphic  rocks. 

Its  crystals  are  mounted  and  used  as  watch  charms. 

94.  Nephelite  ((Na,K)AlSi04) 
is  important  principally  as  a  rock 
constituent.  Its  crystals  are  hexag- 
onal prisms  in  habit  (Fig.  61). 

The  mineral  is  white  or  gray; 
transparent  and  glassy  when  fresh. 
When  occurring   as  grains   in-  old 
rocks,  it  may  be  pink,  brown,  yellowish  or  greenish; 
translucent,  and  greasy  in  luster.     This  form  is  often 


FIG.  61. — Nephelite 
Crystals. 


92  MINERALS  AND  ROCKS 

designated  eleolite.  The  streak  is  always  white.  Its 
hardness  is  5-6  and  sp.gr.  2.6. 

Before  the  blowpipe,  the  mineral  melts  to  a  white 
or  colorless,  bubbly  glass.  Its  powder  before  and  after 
roasting  reacts  alkaline.  It  dissolves  easily  in  HC1 
with  the  production  of  a  voluminous  precipitate  of 
gelatinous  silica. 

Nephelite  is  distinguished  by  its  crystals,  its 
hardness  and  its  gelatinization  with  acids;  eleolite 
by  its  gelatinization  and  greasy  luster. 

It  occurs  in  crystals  implanted  on  the  walls  and 
cavities  in  volcanic  rocks  and  as  grains  in  them. 

The  Micas. — The  micas  are  a  group  of  minerals 
that  are  characterized  by  such  a  very  perfect  cleavage 
in  a  single  direction  that  thin  plates  may  be  split 
from  them  with  ease.  Moreover,  in  the  true  micas 
these  plates  are  elastic;  that  is,  they  may  be  bent 
without  breaking,  and  when  the  bending  force  is  re- 
moved they  fly  back  to  their  original  positions.  Some 
of  the  micas  are  of  great  economic  importance,  but 
for  others  no  use  has  yet  been  found.  Chemically, 
the  micas  are  very  complex.  They  may  be  separated 
into : 

(1)  The  magnesium  iron  micas,  of  which  biotite 

is  the  best  illustration. 

(2)  The  calcium  micas. 

(3)  The  lithium-iron  micas. 

(4)  The  alkaline  micas. 

Of  the  latter  there  are  three  subdivisions: 

(a)  The   lithium    micas,    represented    by    lepi- 

dolite. 

(b)  The  potash  mica,  muscovite. 

(c)  The  soda  mica,  paragonite. 


DESCRIPTION  OF  MINERALS  93 

95.  Biotite  ((K,H)2(Mg,Fe)2(Al,Fe)2(SiO4)3)  is  the 
principal  magnesian  mica.  Its  composition  is  repre- 
sented approximately  by  the  formula  given  above. 
Those  varieties  in  which  Fe  replaces  nearly  all  the 
Mg  are  known  as  lepidomelane.  Those  in  which  Mg 
is  in  great  excess  are  called  phlogopite.  Biotite  in- 
cludes the  remaining. 

The  biotites  occur  in  monoclinic  crystals  with  an 
hexagonal  habit,  in  flat  scales,  and  scaly  aggregates. 

Their  color  varies  from  yellow,  through  green  and 
brown  to  black,  and  they  are  strongly  pleochroic. 
Their  streak  is  white,  luster  glassy,  hardness  2.5 
and  sp.gr.  2.7-3.1.  They  are  transparent  or  trans- 
lucent. 

Before  the  blowpipe,  the  dark,  ferruginous  varieties 
whiten  and  fuse  on  thin  edges  to  a  black  glass;  the 
lighter  colored  ones,  with  greater  difficulty,  to  a  brown 
glass.  In  the  closed  tube,  they  yield  a  little  water 
and  some  varieties  give  the  reaction  for  fluorine  (p. 
155)  in  the  open  tube;  phlogopite,  nearly  always. 
They  are  decomposed  in  strong  H2S04  with  the  sepa- 
ration of  scales  or  flakes  of  Si02. 

All  the  micas  are  easily  distinguished  from  other 
minerals  by  their  perfect  cleavage  into  elastic  folise, 
and  the  biotites  from  the  other  micas  by  their  solu- 
bility in  H2SO4.  Lepidomelane  is  recognized  by  its 
black  color,  biotite  by  its  dark  greenish  or  dark  brown 
color,  and  phlogopite  by  its  amber  color. 

Biotite  and  lepidomelane  occur  as  the  constituents 
of  igneous  rocks  and  of  certain  mica  schists.  Phlogo- 
pite is  especially  characteristic  of  metamorphic  lime- 
stones. 

Phlogopite  is  used    under    the    name    of    amber 


94  MINERALS  AND  ROCKS 

mica  in  the  manufacture  of  certain  electrical  appli- 
ances. The  other  biotites  have  no  commercial  value. 
96.  Muscovite  (H2(K,Na)Al3(Si04)3)  is  the  alkali 
mica  in  which  potassium  predominates.  It  is  one  of 
the  commonest  of  all  the  micas  and  at  the  same  time 
the  most  valuable,  because  of  its  transparency.  It 
occurs  in  tabular  crystals  that  are  orthorhombic  or 
hexagonal  in  habit  (Fig.  62),  in  broad  plates,  and  in 
small  flakes. 

Muscovite  is  Colorless  or  of  some  light  shade  of 
green,  yellow  or  red.     It  has  a  glassy  luster,  a  hard- 
ness of  2  and  a  sp.gr.    of    2.76-3.1. 
It    is  pleochroic.     It   is  a  non-con- 
ductor   of    electricity    at    ordinary 
Muscovite  Crystal,     temperatures,  and  is  a  poor  conductor 

of  heat. 

Before  the  blowpipe,  thin  flakes  of  muscovite 
fuse  on  their  edges  to  a  gray  mass.  In  the  closed  tube, 
the  mineral  yields  water  which,  in  some  cases,  reacts 
for  F.  It  is  insoluble  in  acids. 

It  is  easily  recognized  as  a  true  mica  by  its  elastic 
cleavage  folise  and  is  distinguished  from  the  biotites 
and  ordinary  lepidolite  by  its  color.  From  colorless 
lepidolite  and  paragonite  (Nos.  98,  97),  it  is  distin- 
guished by  the  flame  test  for  K  (p.  144). 

The  mineral  occurs  in  largef  ill-defined  crystals,  in 
coarse  grains,  as  flakes  in  many  igneous  rocks,  in  some 
sandstones  and  slates  and  in  mica  schists.  It  also 
occurs  in  veins  with  other  minerals. 

It  is  employed  in  sheets  for  stove  windows,  gas- 
lamp  chimneys,  insulators  in  electrical  apparatus, 
etc.  Ground  mica  is  used  in  wall  paper,  heavy  lubri- 
cants and  fancy  paints.  It  is  also  mixed  with  shellac 


DESCRIPTION  OF  MINERALS  95 

and  molded  into  shapes  suitable  for  electrical  insu- 
lators. 

97.  Paragonite  (H2(Na,K)Al3(Si04)3)  is  less  com- 
mon   than    muscovite.    It    apparently    occurs    most 
abundantly  in  certain  fine-grained  mica   schists.     It 
can  be  distinguished  from  muscovite  only  by  chemical 
tests. 

98.  Lepidolite    (CLi,K,Na)2((Al,Fe)pH,F)  2(^03)3), 
the  lithium  alkali  mica,  occurs  almost  exclusively  as 
aggregates  of  thin    plates    with    hexagonal    outlines; 
occasionally,  in  tabular  crystals  with  centers  of  mus- 
covite. 

It  is  white,  rose,  light  purple,  gray  or  greenish, 
and  transparent.  Its  streak  is  white,  its  luster  glassy, 
its  hardness  2  and  sp.gr.  2.8-2.9. 

It  fuses  easily  to  a  white  enamel  and  at  the  same 
time  colors  the  flame  crimson  (Li).  It  is  with  diffi- 
culty attacked  by  acids,  but  after  heating  is  easily 
decomposed. 

Lepidolite  is  distinguished  from  the  other  micas 
by  its  color  and  its  reactions  for  Li. 

It  occurs  principally  in  coarse  granite  dikes  and 
near  the  borders  of  granite  masses.  It  is  usually 
associated  with  rubellite  and  other  bright-colored, 
transparent  tourmalines  (No.  108)  and  often  with 
cassiterite  (No.  40). 

Lepidolite  is  utilized  to  a  slight  extent  in  the  prep- 
aration of  lithium  salts,  which  are  employed  in  medi- 
cine, photography  and  in  the  manufacture  of  fireworks 
and  storage  batteries. 

99.  Brittle  micas   differ  from  the  true  micas  in 
that  their  cleavage  folise  are  brittle.     They  are  basic 
silicates  of  Ca,  Mg,  Fe  and  Al,  one  of  the  most  common, 


96  MINEEALS  AND  ROCKS 

cfdorttoid,  being  approximately  H2(Fe,Mg)Al2Si07. 
They  usually  occur  in  plates  and  scales  that  are 
alteration  products  of  other  minerals. 

The  brittle  micas  are  green,  red,  brown  or  yellow, 
with  a  white  streak,  a  hardness  between  4  and  6  and 
a  sp.gr.  between  3.1  and  3.6.  Most  of  them  are  trans- 
parent or  translucent. 

Before  the  blowpipe,  they  whiten  on  their  edges 
and  are  infusible,  or  fusible  with  difficulty.  All  give 
off  water  when  heated  in  the  closed  tube.  Some  are 
decomposed  by  HC1,  but  others  are  unattacked. 

They  are  distinguished  by  their  perfect  cleavage 
and  their  brittleness. 

They  occur  in  metamorphosed  limestone  and  in 
schists. 

100.  Chlorites  are  also  micaceous,  or  scaly,  decom- 
position products.  They  are  hydrous  silicates  of 
Mg,  Fe  and  Al  in  various  proportions.  The  most 
common  are  prochlorite  and  clinochlor.  The  former 
contains  about  15  per  cent.  MgO  and  the  latter  35  per 
cent. 

These  two  chlorites  occur  in  small,  tabular  crys- 
tals in  scaly  aggregates  and  occasionally  in  earthy 
masses. 

They  are  dark  green  in  color,  have  a  white  or  light- 
green  streak,  a  glassy  luster,  and  one  very  perfect 
cleavage.  The  hardness  of  prochlorite  is  between 
1  and  2  and  of  clinochlor  between  2  and  2.5  and  their 
sp.gr.  is  between  2.6  and  2.9. 

Before  the  blowpipe,  they  exfoliate  and  fuse  on 
their  edges.  In  the  closed  tube,  all  yield  water  when 
strongly  heated.  HC1  attacks  them  with  difficulty; 
H2S04  with  ease. 


DESCRIPTION  OF  MINERALS  97 

They  are  distinguished  by  their  cleavage,  color, 
softness,  solubility  in  H2S04  and  manner  of  occurrence. 

They  are  found  as  constituents  of  partially  altered 
igneous  rocks,  and  of  schists.  Chlorite  schists  are 
made  up  largely  of  chlorites  and  quartz  (No.  34).  The 
chlorites  also  fill  veins,  and  form  pseudomorphs  after 
other  minerals. 

101.  Leucite    (KAl(SiOs)2),  is  an  important  rock 
constituent.     It  occurs  almost  exclusively  in  isometric 
crystals,    resembling    those   of  garnet 
(Fig.  63),  or  in  small  round  grains. 

It  is  white  or  light  gray,  with  a 
glassy  luster,  and  a  white  streak.  It 
is  brittle  and  transparent  or  translu- 
cent, and  has  a  hardness  of  5-6  and 
a  sp.gr.  of  2.5.  Because  it  easily  FIG.  63. — Leucite 
decomposes,  most  specimens  appear 
white  and  opaque. 

Before  the  blowpipe,  leucite  is  infusible,  but  colors 
the  flame  for  K.  It  is  soluble  in  HC1  with  the  pro- 
duction of  pulverulent  silica.  Its  powder  reacts 
alkaline. 

Leucite  is  distinguished  from  most  other  minerals 
by  its  crystallization.  It  is  distinguished  from  white 
garnet  (No.  88)  by  its  inferior  hardness  and  from 
analcite  (No.  130)  by  its  infusibility  and  the  fact  that 
it  contains  no  water.  Moreover,  analcite  fails  to  give 
the  flame  reaction  for  K  (p.  144). 

The  mineral  occurs  principally  in  igneous  rocks, 
especially  lavas  that  are  rich  in  potash.  It  has  no 
commercial  value  at  the  present  time,  but  it  has  been 
suggested  that  it  might  be  made  a  source  of  potash 
salts. 


98  MINERALS  AND  ROCKS 

102.  Kyanite,  cyanite  ((AlO)2Si03)  or  disthene 
is  an  abundant  component  of  some  schistose  rocks. 
The  name,  "kyanite",  suggests  the  sky-blue ,  color 
noticed  in  many  specimens,  and  the  name,  "disthene", 
refers  to  the  difference  in  hardness  exhibited  in  different 
directions. 

Kyanite  is  usually  found  in  long,  flat,  isolated 
blades  (Fig.  64)  with  a  perfect  longitudinal  cleavage. 


FIG.  64. — Kyanite  Crystals  in  Quartzite. 

• 

Its  luster  is  glassy,  except  on  cleavage  surfaces,  where 
it  is  pearly. 

The  mineral  is  commonly  light  blue  and  transparent 
or  translucent.  Less  commonly,  it  is  colorless  or  white, 
yellow,  green  or  gray.  Its  hardness  on  the  cleavage 
plane  is  about  5  in  the  longitudinal  direction  and  7 
perpendicular  to  this. 

Before  the  blowpipe,  kyanite  is  infusible.  With 
cobalt  solution,  it  reacts  for  Al  (p.  147).  It  is  insoluble 
in  acids. 


DESCRIPTION  OF  MINERALS 


99 


Kyanite  is  not  easily  confused  with  other  minerals. 
It  is  distinguished  from  the  few  which  it  resembles  by 
the  great  difference  in  hardness  in  different  directions 
on  its  cleavage  faces. 

It  occurs  in  micaceous  schists  and  schistose  quartz- 
ites. 

The  blue  transparent  variety  is  sometimes  used  as 
a  gem. 

103.  Beryl  (BeaAhCSiOaJe),  a  frequent  constituent 
of  coarse-grained  granites,  occurs  in  well-defined 


FIG.  65. — Beryl  Crystals. 


prismatic  hexagonal  crystals  (Fig.  65),  in  some  instances 
of  great  size,  and  in  granular  aggregates  and  massive. 

It  is  colorless  or  light  green,  red  or  blue,  and  is 
transparent  or  translucent.  Its  streak  is  white,  luster 
glassy,  hardness  7  to  8  and  sp.gr.  about  2.7. 

Before  the  blowpipe,  colorless  varieties  become 
milky,  but  others  are  unchanged  except  at  very  high 
temperatures,  when  sharp  edges  are  fused  to  a  porous 
glass.  The  mineral  is  not  attacked  by  acids. 

It  is  distinguished  from  apatite  (No.  72)  by  its 
greater  hardness. 

The  mineral  occurs  as  crystals  or  crystalline  masses 
in  coarse  granites,  in  schists,  in  ore  veins,  in  slates 
and  rarely  in  limestone. 


100  MINERALS  AND  ROCKS 

Its  transparent  varieties  are  used  as  gems  under 
the  following  names: 

Emerald,  a  deep  green  variety. 
Aquamarine,  a  blue-green  variety. 
Golden  beryl,  a  topaz-colored  variety. 
Blue  beryl,  a  blue  variety. 

104.  Serpentine  (H4Mg3Si209)  is  a  common  alter- 
ation product  of  olivine  (No.  85),  pyroxenes  (Nos. 
110,  111),  and  a  few  other  silicates.  It  occurs  prin- 
cipally in  fibers  filling  veins  (chrysolite),  as  scales,  and 
massive. 

It  is  white,  gray,  brown,  or  green,  with  a  white 
streak  and  a  dull,  slightly  glistening  or  greasy  luster. 
The  variety  known  as  noble  serpentine  is  nearly 
transparent  and  has  a  clear  greenish  or  yellowish- 
white,  yellowish-green,  apple-green,  or  dark  green 
color.  Other  varieties  are  translucent  or  opaque. 
When  pure,  its  hardness  is  3  and  its  sp.gr.  about  2.6. 

Before  the  blowpipe,  the  mineral  fuses  on  thin 
edges.  It  yields  water  in  the  closed  tube,  reacts  for 
Mg  (p.  147),  and  is  decomposed  by  HC1  and  H2S04 
with  the  separation  of  gelatinous  silica.  Its  powder 
reacts  alkaline. 

Serpentine  is  distinguished  from  steatite  (No.  105) 
by  its  solubility  in  HC1  and  its  greater  hardness. 

The  fibrous,  nearly  transparent,  white  serpentine, 
known  as  chrysotile,  is  mined  as  asbestus.  It  is  dis- 
tinguished from  amphibole  asbestus  (No.  115)  by  the 
test  for  water.  Massive  varieties  are  used  as  building 
stone,  or  are  ground  and  used  as  a  paper  filler,  etc. 
The  finer  varieties  are  sawed  into  slabs  and  these 
are  employed  for  interior  decoration.  The  various 
uses  of  asbestus  are  too  well-known  to  need  mention. 


DESCRIPTION  OF  MINERALS   \     \  :j/:^Wl 

105.  Talc  or  steatite  (H2Mg3(Si03)4)  is  usually 
found  in  flaky,  foliated  and  massive  forms,  and  at  a 
few  places  in  small  acicular  or  prismatic  crystals.  It 
is  an  important  economic  product. 

The  mineral  is  white,  gray,  greenish  or  bluish  and 
is  transparent  or  translucent.  Its  streak  is  white. 
The  massive  forms,  known  as  soapstone,  are  white, 
gray  or  some  other  light  shade.  All  varieties  are  soft 
(H  =  l)  and  all  have  a  soapy  feeling.  The  sp.gr.  of 
the  pure  talc  is  2.6-2.8. 

Before  the  blowpipe,  talc  exfoliates,  hardens  and 
glows  brightly,  but  it  is  nearly  infusible,  melting  only 
on  the  thinnest  edges  to  a  white  enamel.  It  yields 
water  in  the  closed  tube,  only  at  a  high  temperature. 
It  is  unattacked  by  acids  before  and  after  heating. 

It  is  distinguished  from  other  white,  soft  minerals  by 
its  insolubility  in  acids,  and  the  reaction  for  Mg  (p.  147). 

Talc  occurs  as  large  plates  and  groups  of  plates  in 
metamorphosed  limestone,  as  fibers  in  schists,  as 
veins  cutting  serpentine  (No.  104),  as  layers  com- 
posed of  talc  and  quartz  (talc  schist),  associated  with 
other  schistose  rocks,  and  as  pseudomorphs  after  other 
minerals.  Soapstone  occurs  in  rock  masses. 

The  white  talc  is  ground  and  used  as  a  lubricator, 
a  toilet  powder,  a  filler  in  cloth,  paper,  etc.  Soap- 
stone  is  sawed  into  slabs  and  employed  in  lining  acid 
vats,  laundry  tubs,  making  electric  switchboards,  and 
for  many  other  uses  requiring  a  non-absorbent  and 
infusible  material. 

106.  Kaolinite  (H4Al2Si209)  is  one  of  the  principal 
ingredients  of  clay.  As  such,  it  is  of  great  economic 
value.  It  occurs  in  tiny,  thin  tabular  crystals  and  in 
scaly,  foliated  and  earthy  aggregates. 


102  MINERALS  AND  ROCKS 

When  pure,  it  is  white  or  colorless  and  transparent. 
In  masses  it  is  earthy;  in  crystals,  glassy.  Its  hard- 
ness is  1,  and  its  sp.gr.  2.5. 

Before  the  blowpipe,  kaolinite  is  infusible.  It  is 
only  slightly  attacked  by  acids,  but  is  decomposed 
by  alkalies  and  alkaline  carbonates  with  the  separa- 
tion of  gelatinous  silica.  In  the  closed  tube,  it  yields 
water  when  heated. 

It  is  characterized  by  its  softness,  insolubility  in 
acids  and  by  the  Co(N03)2  test  for  Al  (p.  147).  It  is 
distinguished  from  chalk  (No.  50)  by  its  reaction  to- 
ward HC1,  from  infusorial  earth  (No.  42)  by  its  softness, 
and  from  talc  (No.  105)  by  the  reactions  for  aluminium. 

Kaolin  is  an  earthy,  friable  mass  of  kaolinite  which 
becomes  plastic  when  moistened. 

Clay  is  a  mixture  of  kaolinite  and  other  flaky  and 
fibrous  minerals.  The  greater  the  proportion  of  kao- 
linite in  it  the  more  plastic  it  is  and,  consequently,  the 
more  valuable. 

Since  kaolinite  is  a  weathering  product  of  other 
silicates,  it  occurs  in  little  masses  through  rocks.  It 
is  found  also  in  layers  and  pockets  of  nearly  pure 
material. 

Kaolin  and  clay  are  used  in  the  manufacture  of 
pottery,  brick,  tile,  etc. 

107.  Calamine  (ZnOH)2Si03  is  an  ore  of  zinc. 
While  theoretically  a  pure  zinc  compound,  it  usually 
contains  also  a  little  iron  and  frequently  some  lead. 
It  occurs  in  small  brilliant,  tabular  crystals  (Fig.  66), 
implanted  on  the  walls  of  zinc  and  lead  ores.  Often, 
many  crystals  are  grouped  in  fibrous  or  warty  aggre- 
gates and  in  crusts.  It  is  found  also  in  granular  and 
compact  masses. 


DESCRIPTION  OF  MINERALS  103 

The  mineral  is  glassy,  transparent  or  translucent; 
and  when  pure  is  colorless  or  white.     Usually,  however, 
it  is  gray,  yellow,  brown,  greenish  or  blue.     Its  streak 
is  white,  its  hardness,  4-4.5,  and  its  sp.gr. 
3.4.     It    is    brittle    and  strongly    pyro- 
electric,    and  it  becomes  phosphorescent 
when  rubbed. 

Before  the  blowpipe,  it  is  almost  in- 
fusible, but  on  charcoal  it  swells  and  colors 
the  flame  greenish.  When  fused  with 
Na2COs,  it  gives  the  zinc  sublimate  (p.  147) 
which,  when  heated  and  moistened  with 
Co(NOs)2  solution,  changes  to  green.  In 
the  closed  glass  tube,  it  decrepitates,  yields  water 
and  becomes  cloudy.  It  dissolves  in  weak  acids  with 
the  production  of  gelatinous  silica. 

Calamine  is  distinguished  from  smithsonite  (No. 
54)  by  its  reaction  for  acids  and  from  other  minerals 
by  its  crystallization  and  the  reaction  for  zinc  (p.  147). 

Calamine  is  found  principally  in  veins  with  other 
zinc  ores,  with  which  it  is  mined. 

108.  Tourmaline  (R'oAlaCB-OH^Si^io),  in  which 
R'  =  H,  Na,  Li,  Mg,  Cr,  Al,  Fe,  is  a  common  mineral 
of  very  complex  composition.  It  is  more  properly 
the  name  of  a  group  of  compounds  that  occur  mixed 
in  many  proportions.  The  mineral  occurs  in  hand- 
some prismatic  and  acicular  crystals,  nearly  all  of  which 
have  a  triangular  cross-section  (Fig.  67). 

Their  colors  are  varied,  depending  upon  their 
composition.  Those  in  which  the  alkalies  predominate 
are  colorless,  red,  blue  or  green  and  transparent. 
Those  in  which  iron  predominates  are  black  and  trans- 
lucent. Magnesium  varieties  are  yellowish-brown  and 


104 


MINERALS  AND  ROCKS 


translucent  and  chromium  varieties,  dark  green,  black 
and  translucent,  or  colorless  and  transparent. 
The  varieties  designated  by  distinct  names  are: 

Ordinary,  black  or  brown. 

Rubellite,  pink  or  red. 

Indicolite,  blue  or  blue-black. 

Brazilian  sapphire,  blue  and  transparent. 

Brazilian  emerald,  green  and  transparent. 

Peridot  of  Ceylon,  honey-yellow  and  transparent. 

Achroite,  colorless  and  transparent. 
Tourmaline,    whatever   its    color,    is   brittle.     Its 
luster  is  glassy,  and  its  streak  is  white.     It  has  no 


\ 


FIG.  67. — Tourmaline  Crystals. 


distinct  cleavage.  Its  fracture  is  conchoidal.  Its 
hardness  is  7-7.5  and  its  sp.gr.  3-3.2.  The  color, 
in  many  instances,  differs  in  different  portions  of  the 
same  crystal,  the  arrangement  in  some  cases  being 
concentric.  The  mineral  is  strongly  pleochroic;  i.e., 
it  possesses  different  colors  when  looked  through  in 
different  directions. 

Its  behavior  before  the  blowpipe  varies  widely. 
Alkaline  varieties  are  nearly  infusible.  Iron  varieties 
fuse  with  difficulty  and  magnesium  varieties  easily 
to  a  bubbly  glass.  When  fused  with  a  mixture  of 
HKS04  and  powdered  fluorspar,  the  mineral  gives  a 
distinct  reaction  for  boron  (p.  152). 


DESCRIPTION  OF  MINERALS 


105 


When  in  crystals,  tourmaline  is  easily  recognized 
by  its  form.  Massive  brown  varieties  resemble  closely 
vesuvianite  and  garnet  (Nos.  109,  88).  The  boron  test 
identifies  it. 

Tourmaline  occurs  in  quartz  and  ore  veins,  in 
metamorphosed  limestones,  in  schists  and  in  granites 
and  other  coarse-grained  rocks.  The  lithium  varieties 
are  usually  associated  with  the  pink  mica,  lepidolite 
(No.  98). 

The  transparent  tourmalines  are  used  as  gems;  the 
dark  translucent  varieties  in  the  manufacture  of  optical 
instruments. 

109.  Vesuvianite  is  a  complex  mixture  of  basic 
calcium-aluminium  silicates  often  containing  some 
fluorine.  It  occurs  both  massive  and  crystallized. 


FIG.  68. — Vesuvianite  Crystals. 

Its  crystals  are  columnar  (Fig.  68),  pyramidal  or 
acicular,  usually  with  a  square  or  octagonal  cross- 
section.  They  possess  no  distinct  cleavage. 

Vesuvianite  is  glassy  in  luster  and  yellowish, 
greenish  or  brownish  in  color.  It  is  transparent  or 
translucent  and  its  streak  is  colorless.  A  rare  green  or 
gray  and  green  translucent  massive  variety  is  known 
as  calif ornite.  Its  hardness  is  6-7  and  sp.gr.  3.3-3.5. 

Before  the  blowpipe,  vesuvianite  melts  to  a  brown 
or  green  glass.  It  is  decomposed  with  difficulty  by 


106  MINERALS  AND  ROCKS 

acids,  but  after  being  heated  it  dissolves  slowly  with 
the  separation  of  gelatinous  silica. 

Vesuvianite  is  identified  when  in  crystals  by  its 
form.  Massive  varieties  are  apt  to  be  confused  with 
garnet,  tourmaline  and  epidote  (Nos.  88,  108,  92). 
They  are  distinguished  from  the  latter  by  their  much 
easier  fusibility. 

The  mineral  is  found  as  crystals  on  the  walls  of 
veins,  where  it  is  associated  with  quartz,  calcite, 
garnet  and  ore  minerals,  and  as  grains  in  metamor- 
phosed limestones  and  in  crystalline  schists. 

Californite  and  a  blue  variety,  containing  copper 
and  known  as  cyprine,  are  used  as  gems. 

PYROXENES   AND    AMPHIBOLES 

The  pyroxenes  and  amphiboles  comprise  a  large 
group  of  complex  silicates  that  crystallize  in  various 
systems  with  different  habits.  The  amphiboles  are 
distinguished  by  having  a  prismatic  cleavage  inter- 
secting at  angles  of  56°  and  124°  and  the  pyroxenes 
by  possessing  a  similar  cleavage  intersecting  at  about 
87°  and  93°.  They  are  all  silicates  of  Mg,  Ca  or  Fe, 
with  alkalies,  Mn  and  Al,  in  certain  cases. 

The  pyroxenes  are  widely  spread  as  the  constit- 
uents of  igneous  rocks  and  of  veins  that  have  been 
filled  by  igneous  processes.  Their  crystals  are  usually 
prismatic,  with  a  distinct  cleavage  parallel  to  two  of 
the  prismatic  planes.  Their  cross-sections  are  repre- 
sented in  Fig.  69a.  The  best-known  pyroxenes  are 
bronzite,  augite  and  spodumene. 

110.  Bronzite  ((Mg,Fe)Si03)  is  a  mixture  of  MgSiO3, 
which  is  known  as  enstatite,  and  FeSiOa,  known  as 


DESCRIPTION  OF  MINERALS  107 

hypersthene.    The  three  minerals  are  found  as  crystals, 
fibrous  and  lamellar  masses  and  plates. 

The  color  of  bronzite  varies  with  the  proportion  of 
Mg  and  Fe  present.  Enstatite  is  light  gray,  yellow 
or  green;  bronzite,  brown,  purple  or  green;  and  hypers- 
thene, black,  dark  purple  or  dark  green.  All  varieties 
have  a  colorless  streak,  and  many  show  a  metallic 
shimmer  on  certain  planes.  The  hardness  of  enstatite 
is  5.5  and  its  sp.gr.  3.2.  The  corresponding  proper- 
ties of  hypersthene  are:  H  =  5-6;  sp.gr.  =  3.45. 


<*•  &. 

FIG.  69. — Cross-sections  of  Pyroxenes  (a)  and  Amphiboles  (6). 

Before  the  blowpipe,  the  iron-free  members  are 
infusible.  With  increase  in  iron,  the  ease  of  fusibility 
increases,  nearly  pure  hypersthene  fusing  to  a  greenish- 
black,  weakly  magnetic  glass.  When  treated  with 
HC1,  the  members  near  enstatite  are  unattacked  and 
those  near  hypersthene  are  slightly  decomposed. 

When  in  crystals,  bronzite  is  easily  recognized  by 
its  forms  and  cleavage.  Massive  and  fibrous  varieties 
must  be  recognized  by  their  general  appearance  and 
their  manner  of  occurrence. 

They  weather  to  serpentine,  tale  (Nos.  104,  105), 
and  amphibole. 

These  pyroxenes  are  found  in  igneous  rocks  and  in 
veins. 


108  MINERALS  AND  ROCKS 

111.  Augite  is  a  Mg-Fe-Ca  pyroxene  contain- 
ing Al.  It  may  be  represented  as  a  mixture  of 
(Mg,Fe)Ca(Si03)2  and  (Mg,Fe)(Al,Fe)2Si06.  It 
occurs  as  crystals  and  grains  in  igneous  rocks,  in 
schists,  and  in  veins  with  ore  minerals,  especially  mag- 
netite (No.  47). 

Its  crystals  are  short,  prismatic  (Fig.  70),  and  have 
the  usual  prismatic  cleavage.  They  are  all  glassy  in 
luster  and  their  color  varies  with  their  composition, 
greenish  and  purplish-black  tints  predominating. 


FIG.  70.— Augite  Crystals. 

Their  streak  is  white;  hardness  5-6  and  sp.gr.  about 
3.5. 

Before  the  blowpipe,  augite  is  fusible,  the  ease  of 
fusibility  increasing  with  the  amount  of  iron  present. 
It  is  insoluble  in  acids. 

Augite  is  distinguished  from  other  silicates  by  its 
crystallization  and  cleavage. 
The  principal  varieties  are: 
Fassaite,  pale  to  dark  green. 
Augite,  dark  green  or  brownish-black.     Sp.gr. 

3.24. 

Diallage,  characterized  by  a  distinct  parting  in 
addition  to  the  usual  prismatic  cleavage,  and 
a  lamellar  structure. 

Under  the  influence  of  surface  agencies,  augite  alters 
to  hornblende  (No.  116),  the  corresponding  amphibole, 


DESCRIPTION  OF  MINERALS  109 

and  to  serpentine  (No.  104),  to  chlorites  (No.  100),  and 
other  hydrous  compounds. 

112.  Spodumene  ((Li,  Na)Al(SiO3)2)  is  an  alkaline 
pyroxene  which  is  used  to  some  extent  as  a  source  of 
lithium    compounds.     It    occurs    as    large    columnar 
or  tabular   crystals    (Fig.   71)  which  are 
striated  vertically,  and  as  platy  or  scaly 
aggregates.     Its  cleavage  is  perfect,  as  in 
the  other  pyroxenes. 

The  mineral  has  a  glassy  luster,  ap- 
proaching pearly  on  cleavage  surfaces.  It 
is  white,  greenish,  or  amethystine  in  color 
and  its  streak  is  white.  It  is  transparent 
or  translucent,  has  a  hardness  between  6  Crystal. 
and  7  and  a  density  of  3.2. 

Before  the  blowpipe,  it  swells  and  fuses  to  a  color- 
less glass,  at  the  same  time  imparting  a  crimson  tinge 
to  the  flame.  It  is  unattacked  by  acids.  Its  powder 
reacts  alkaline. 

It  is  characterized  by  its  cleavage,  and  the  color 
it  imparts  to  the  flame.  It  has  a  higher  sp.gr.  than 
feldspar  (Nos.  118-120)  and  is  less  fusible  than  am- 
Uygonite — a  lithium  phosphate. 

Spodumene  occurs  as  crystals  and  grains  in  gran- 
ites and  crystalline  schists. 

The  ordinary  varieties  are  used  in  manufacturing 
lithium  salts  and  the  transparent  varieties  as  gems. 
Of  the  latter,  hiddenite  is  emerald-green  and  glassy; 
and  kunziie,  pink  or  lilac. 

The  amphiboles,  like  the  pyroxenes,  occur  in  igneous 
and  sedimentary  rocks  and  as  the  fillings  of  veins. 
They  occur  also  as  frequent  components  of  schists 
and  other  metamorphic  rocks.  The  most  common 


110 


MINERALS  AND  ROCKS 


members  of  the  group  are  tremolite,  actinolite,  horn- 
blende and  glaucophane.  All  the  amphiboles  are 
found  in  crystals  (Fig.  72),  some  of  which  have  the 
same  habit  as  pyroxene  crystals ;  most  of  them,  how- 
ever, are  more  acicular.  Their  cross-sections  are 
illustrated  in  Fig.  695. 

113.  Tremolite  (Mg3Ca(Si03)4),  though  occasion- 
ally in  crystals,  is  more  frequently  found  in  long 
needles  or  plates. 

The  mineral  is  white  or  light  green  and  transpar- 


FIG.  72. — Amphibole  Crystals. 

ent  or  translucent.  Its  luster  is  glassy;  its  streak 
white;  its  hardness  about  5.5,  and  its  sp.gr.  about  3. 

Before  the  blowpipe,  tremolite  fuses  only  on  thin 
edges.  It  is  unattacked  by  acids.  Its  powder,  es- 
pecially after  roasting,  reacts  alkaline.  It  gives  a 
pink  reaction  for  Mg  with  Co(N03)2  solution. 

Tremolite  is  characterized  by  its  acicular  crystals, 
color,  cleavage  and  the  reaction  for  Mg. 

It  occurs  principally  in  metamorphosed  limestones. 

114.  Actinolite  differs  from  tremolite  in  containing 
a  notable  quantity  of  ferrous  iron.  It  is  light  or  dark 
green  and  has  a  very  light  streak.  Its  sp.gr.  is  3.1. 
It  is  usually  in  thin,  needle-like  crystals  or  in  fibrous 
or  granular  aggregates. 

When  heated  before  the  blowpipe  or  on  charcoal, 
it  fuses  with  difficulty  to  a  magnetic  bead. 


DESCRIPTION  OF  MINERALS  111 

Actinolite  is  especially  common  in  schists.  In 
some,  it  occurs  in  such  large  quantiy  as  to  consti- 
tute their  principal  component.  Actinolite  schists  are 
rocks  composed  essentially  of  actinolite  and  quartz. 

115.  Asbestus  is  a  fibrous  variety  of  tremolite  or 
actinolite.     It  occurs  principally  in  limestones  and  a 
few  other  rocks  which  have  been  crushed  and  sheared. 
It  has  the  same  uses  as  chrysotile  asbestus  (No.  104),  but 
is  not  regarded  with  as  much  favor  because  less  pliable. 

116.  Hornblende  occupies  the  same  position  among 
the  amphiboles  as  does  augite  among  the  pyroxenes. 
It  is  the  aluminous  amphibole  composed  of  a  mixture 
of  (Mg,Fe)3Ca(Si03)4  and  (Mg,Fe)((Al,Fe)O)2Si04. 

It  occurs  usually  in  short,  prismatic  crystals  (see 
Fig.  72)  with  the  habit  of  those  of  augite,  in  long 
acicular  or  platy  crystals  and  in  granular  masses. 
It  possesses  the  distinct  amphibole  cleavage  of  56° 
and  124°,  by  which  it  is  distinguished  best  from  augite. 
Hornblende  is  black  or  dark  green,  with  a  glassy 
luster,  a  white  streak,  a  hardness  of  5.5  and  a  sp.gr.  of 
3-3.5,  depending  upon  the  proportion  of  the  iron 
molecule  present. 

Before  the  blowpipe,  it  fuses  with  difficulty  on 
thin  edges.  Heated  on  charcoal,  it  gives  a  magnetic 
globule.  It  is  unattacked  by  acids. 

It  is  best  recognized  by  its  crystallization  and 
cleavage. 

Several  varieties  are  designated  by  distinct  names: 
Common  hornblende  is  greenish-black. 
Edenite  is  white,  gray  or  light  green.     It  con- 
tains very  little  iron. 

Basaltic  hornblende  is  black.     It  contains  much 
ferric  iron. 


112  .  MINERALS  AND  ROCKS 

Hornblende  occurs  in  igneous  and  metamorphic 
rocks  and  also  as  a  constituent  of  veins.  In  some 
schists — the  amphibolites — it  is  the  predominant  com- 
ponent. In  others — the  hornblende  schists — it  is  asso- 
ciated with  quartz. 

117.  Glaucophane  differs  in  appearance  from  ordi- 
nary hornblende  in  that  it  is  blue,  purple,  or  bluish- 
black.  It  is  essentially  a  mixture  of  NaAl(SiO)3 
and  (Fe,Mg)SiOs.  It  rarely  occurs  in  crystals,  but 
usually  is  in  grains  and  plates  in  schistose  rocks. 

Glaucophane  is  translucent  and  strongly  pleo- 
chroic.  Its  streak  is  gray-blue,  it  hardness  about 
6  and  its  sp.gr.  about  3. 

Before  the  blowpipe,  it  turns  brown  and  then 
melts  to  an  olive-green  glass,  coloring  the  flame  for 
sodium.  It  is  with  difficulty  attacked  by  acids. 

Glaucophane  is  distinguished  from  other  amphi- 
boles  by  its  color,  and  from  other  blue  silicates  by  its 
hardness  and  manner  of  occurrence. 

It  is  an  essential  constituent  of  glaucophane 
schists  and  an  accessory  component  in  other  meta- 
morphic rocks. 

FELDSPAKS 

This  group  consists  of  minerals  that  are  essentially 
alumino-silicates  of  the  alkalies  and  calcium,  rarely 
also  of  barium.  There  are  two  sub-groups  distin- 
guished by  their  methods  of  crystallization.  In  one, 
the  two  cleavages,  which  are  present  in  all  feldspars, 
are  perpendicular  to  one  another.  The  group  is 
apparently  monoclinic.  In  the  other  group,  the 
cleavages  are  inclined  at  an  angle  that  departs  slightly 
from  90°.  This  group  is  triclinic. 


DESCRIPTION  OF  MINERALS  113 

All  the.  feldspars  are  light-colored  when  pure,  and 
translucent  or  transparent,  and  all  have  a  white 
streak.  Nearly  all  are  insoluble  in  acids  and,  with 
difficulty,  fusible  before  the  blowpipe.  They  possess 
two  distinct  cleavages  that  yield  fairly  smooth,  glist- 
ening surfaces.  Their  hardness  is  6  and  their  sp.gr. 
varies  between  2.55  and  3.34. 

The  feldspars  are  easily  distinguished  from  nearly 
all  other  silicates  by  their  color,  hardness  and  easy 
cleavage  into  platy  fragments  with  glistening  surfaces. 

Feldspars  occur  in  veins,  in  ore  bodies  and  as 
components  of  many  igneous  and  metamorphic  rocks. 
Pegmatite  is  a  coarse-grained  rock  occurring  in  veins, 
and  consisting  of  feldspar,  quartz  and  usually  mica  or 
hornblende. 

Though  abundant,  the  feldspars  have  comparatively 
few  uses.  In  the  future,  the  potash  varieties  may 
become  sources  of  the  potash  salts  used  in  fertilizers, 
but  at  present  their  principal  uses  are  in  the  manu- 
facture of  porcelain,  and  other  white  pottery  prod- 
ucts and  of  enamel  ware.  They  are  used  also  as 
fluxes  and  are  employed  in  making  opalescent  glass, 
scouring  soaps,  window  washes  and  ready  roofing. 

118.  Orthoclase  (KAlSi308)  is  the  principal  mono- 
clinic  feldspar.  It  is  one  of  the  two  potassium  feld- 
spars; the  other,  microcline,  being  triclinic.  It  occurs 
in  crystals  and  in  crystalline  grains. 

The  crystals  are  simple  and  twinned.  Simple 
crystals  are  all  more  or  less  prismatic  (Fig.  73) .  Their 
habits  are  equidimensional,  columnar  or  tabular. 
Twinned  crystals  are  of  several  kinds.  Carlsbad 
twins  consist  of  two  crystals  intergrown,  as  in  Fig. 
74  a.  Baveno  twins  are  columnar  groups  of  parts  of 


114  MINERALS  AND  ROCKS 

two  crystals  grown  together  along  a  plane  parallel 
to  the  columnar  axis,  as  in  Fig.  74  b.  The  result  of 
this  twinning  is  a  square  prism,  with  its  ends  crossed 
by  a  diagonal  that  separates  the  two  individuals. 


FIG.  73.— Simple  Crystals  of  Orthoclase. 

Orthoclase  may  be  colorless  or  light-colored,  trans- 
parent or  translucent.  Its  cleavage  is  perfect,  or 
nearly  so,  in  two  perpendicular -directions.  Its  sp.gr. 
is  2.55. 

Before  the  blowpipe,  fragments  of  orthoclase  are 
with  difficulty  fusible  on  their  edges  to  a  porous 


a.  6. 

FIG.  74. — Twinned  Crystals  of  Orthoclase. 

glass,  at  the  same  time  coloring  the  flame  violet  (K). 
The  mineral  is  insoluble  in  HC1. 

Orthoclase  alters  readily  to  kaolin  and  quartz  and 
to  muscovite  (Nos.  106,  34,  96). 


DESCRIPTION  OF  MINERALS  115 

Several    varieties    are    designated    by   distinctive 
names : 

Adularia  is  a  transparent  variety,  occurring  in 
veins.     Its  crystals  are  of  a  different  habit 
from  those  of  other  orthoclases. 
Moonstone  is  a  translucent  adularia,  exhibiting 

a  pearly  luster. 

Sanidine  is  a  glassy  ortho'clase  containing  some 
soda,  which  occurs  in  large,  flat  crystals  in 
certain  lavas. 

Sunstone  is  a  translucent  variety,  exhibiting 
reddish  flashes  from  inclusions  of  mica  or 
other  platy  minerals. 

Perthite  is  a  group  of  parallel  intergrowths  of 
thin  lamellae  of  orthoclase  and  albite  (Nos.  118 
and  120). 

The  principal  use  of  orthoclase  is  in  the  pottery 
industry. 

119.  Microcline  (KAlSisOg)  differs  from  orthoclase 
mainly  in  its  crystallization.     It  is  triclinic  and  nearly 


FIG.  75. — Thin  Section  of  Microcline  as  Seen  between  Crossed  Nicols. 
(After  Iddings.) 

always  twinned  in  such  a  way  that  thin  sections, 
when  viewed  in  polarized  light  between  crossed  nicols, 
exhibit  series  of  light  and  dark  bars  crossing  one 
another  perpendicularly  (Fig.  75).  This  grating  struc- 
ture is  not  visible  to  the  unaided  eye. 


116  MINERALS  AND  ROCKS 

The  ordinary  physical  and  chemical  properties  of 
microcline  are  the  same  as  those  of  orthoclase  and, 
consequently,  the  two  minerals  can  be  distinguished 
only  by  crystallographic  or  optical  means. 

Microcline  is  a  common  constituent  of  Jcertain 
igneous  rocks  and  crystalline  schists  and  of  some 
pegmatites. 

120.  Plagioclase. — This  name  is  given  to  the  series 
of  soda-calcium  feldspars,  all  of  which  are  triclinic. 
Their  cleavages  are  inclined  to  one  another  at  angles 
that  depart  slightly  from  90°.  Nearly  all  the  plagi- 
oclases  contain  small  quantities  of  potassium.  The 
members  of  the  series  with  their  compositions  and 
sp.gr.  are  as  follows: 

Albite  NaAlSi308(Ab)  Si02  =  68.7%  Sp.gr.  =  2.605 

Oligodase  AbeAn-AbsAn  Si02=62.0%  Sp.gr.  =2.649 

Andesine  AbsAn  -AbAn  Si02  =55.6%  Sp.gr.  =2.679 

Labradorite  AbAn  -  AbAn3  Si02  =49.3%  Sp.gr.  =2.708 

Bytownite  AbAn3  -  AbAne  Si02  =  46.6%  Sp.gr.  =2.742 

Anorthite  CaAl2(Si04)2(An)  Si02=43.2%  Sp.gr.  =2.765 

Albite,  the  pure  or  nearly  pure,  soda  plagioclase, 
contains  68.7%  SiCb  and  anorthite,  the  calcium  plagio- 
clase, contains  43.2%  8162.  Thus,  albite  contains  more 
of  the  acid  radical  than  does  anorthite  and  is,  therefore, 
said  to  be  more  acid.  On  the  other  hand,  anorthite 
is  said  to  be  more  basic.  The  other  members  of  the 
group  are  mixtures  of  these  two  in  the  proportions 
designated  in  the  table  (thus,  andesine  includes  those 
plagioclases  containing  between  one  and  three  parts  of 
albite  to  one  of  anorthite).  Their  relative  acidity  is 
indicated  by  their  position  in  the  table  with  respect 
to  albite  and  anorthite,  or  by  the  proportion  of  the 
albite  molecule  in  the  mixture.  The  percentages  of 


DESCRIPTION  OF  MINERALS 


117 


given  correspond  to  those  mixtures  opposite 
each  name  containing  the  smallest  proportion  of 
albite.  Thus,  andesine  is  more  acid  than  labradorite 
and  it  contains  from  55.6%  to  62%  of  Si02. 

Crystals  of  the  plagioclases  are  like  those  of  ortho- 
clase.  The  soda-rich  members  usually  contain  many 
planes.  The  lime-rich  members  are  simpler.  Twins, 
like  those  of  orthoclase,  are  not  uncommon,  but  much 
more  common  are  the  albite  and  pericline  twins,  which 
are  of  a  different  type.  Albite  twins  are  made  up 


FIG.  76. — Albite  Twins  of  Plagioclase. 

of  two  or  many  parallel  plates  that  are  arranged  per- 
pendicularly to  the  most  perfect  cleavage  (see  Fig.  76). 
Therefore,  the  most  perfect  cleavages  across  plagio- 
clases twinned  according  to  this  plan  exhibit  parallel 
striations  when  examined  in  light  reflected  at  the 
proper  angles  (Fig.  77).  In  the  pericline  twins,  there 
are  also  alternations  of  lamellae,  but  their  positions 
are  such  that  they  are  perpendicular,  or  nearly  so, 
to  the  positions  of  the  albite  lamellae.  Frequently, 
both  methods  of  twinning  are  observed  in  the  same 
specimen;  in  which  case,  the  two  sets  of  striations  can 
be  seen  crossing  each  other  at  angles  of  90°  or  there- 
about (Fig.  78).  Microcline,  though  not  a  plagioclase, 
exhibits  this  double-twinning  clearly  (compare  Fig.  75). 


118 


MINERALS  AND  ROCKS 


The  plagioclases  resemble  very  closely  orthoclase 
and  microcline  in  their  general  character,  though 
pinkish  and  greenish  shades  are  rare.  Their  densities 


FIG.    77. — Twinning   Striations   on   Cleavage   Surface   of   Oligoclase. 
Natural  Size. 

vary  with  their  composition,  as  indicated  in  the  table. 
They  are  usually  translucent,  but  in  some  cases  are 
transparent.  Albite  often  exhibits  a  pearly  luster 
and  often  a  bluish  shimmer.  Oli- 
goclase affords  the  handsomest  sun- 
stones.  The  most  brilliantly  colored 
plagioclases  are  some  forms  of  lab- 
radorite,  which  on  cleavage  surfaces 
show  a  great  display  of  yellow,  green, 
red,  purple,  and  blue  flashes  in 
reflected  light.  The  colors  are  sup- 
posed to  be  due  to  the  presence  of 
numerous,  tiny,  parallel,  acicular  in- 
clusions, which  act  upon  the v  light  in 
the  same  way  as  the  lines  in  a  diffraction  grating. 

Before  the  blowpipe,  all  plagioclases  fuse  to  a  white 
or  colorless  glass,  at  the  same  time  coloring  the  flame 
yellow  (albite)  or  yellowish-red  (anorthite) .  Albite  is 


FIG.  78. 
Crossed  Twinning 

Striations  on 
Plagioclase  Crystal. 


DESCRIPTION  OF  MINERALS  119 

unattacked  by  HC1,  but  anorthite  is  decomposed  by 
this  reagent  with  the  separation  of  gelatinous  or  pul- 
verulent silica.  The  intermediate  members  of  the 
series  are  more  or  less  easily  decomposed,  as  they  con- 
tain more  or  less  of  the  anorthite  molecule. 

The  plagioclases  are  best  distinguished  from  ortho- 
clase  and  microcline  by  the  colors  imparted  to  the  blow- 
pipe flame  and  by  the  twinning  striations  on  their 
cleavage  surfaces.  The  best  means  of  distinguishing 
the  plagioclases  from  one  another  are  their  specific 
gravities. 

The  plagioclases  weather  to  kaolin  (No.  106)  and 
mica  (Nos.  96,  97)  mixed  with  quartz  and  calcite  (Nos. 
34,  50) .  In  rock  masses,  they  often  change  to  a  dark 
gray  mixture  of  epidote,  garnet  and  other  silicates 
known  as  saussurite. 

Albite  occurs  in  vein  masses,  in  metamorphic  rocks 
and  rarely  in  igneous  rocks.  Oligoclase  and  andesine 
occur  in  granite  and  other  siliceous  igneous  rocks  and 
labradorite,  bytownite  and  anorthite  in  the  more  basic 
rocks  like  basalt  and  gabbro  (p.  197).  Anorthite  is 
also  found  in  meteorites. 

Albite  is  mined  from  pegmatite  veins  for  use  in  the 
manufacture  of  pottery.  A  few  of  the  other  plagio- 
clases are  employed  as  gem  stones. 

Hydrated  Silicates 

121.  Chrysocolla  (H2CuSi04-H20),  an  acid  hy- 
drate of  copper,  is  an  important  ore  in  some  places.  It 
occurs  either  massive  or  in  globular  groups  of  fibers. 

It  is  commonly  a  greenish-blue,  translucent,  opal- 
like  or  earthy  mass  with  a  greenish- white  streak. 
Impure  varieties  may  be  brown  or  black,  with  a  dark 


120  MINERALS  AND  ROCKS 

brown  or  dark  green  streak.  It  has  a  conchoidal 
fracture  and  is  brittle.  Its  hardness  varies  between 
2  and  4  and  its  sp.gr.  between  2  and  2.2.  > 

The  mineral  is  infusible  before  the  blowpipe,  but 
colors  the  flame  green.  It  blackens  and  yields  water 
in  the  closed  tube,  and  is  decomposed  by  HC1  with  the 
production  of  pulverulent  silica.  The  solution  reacts 
for  Cu. 

It  is  distinguished  from  other  green  and  blue 
silicates  except  malachite  (No.  60)  by  the  green  color 
it  imparts  to  the  flame.  From  turquoise  (No.  78)  it  is 
distinguished  by  inferior  hardness  and  the  absence  of 
phosphorus. 

Chrysocolla  is  found  in  veins  with  other  copper 
minerals,  and  as  crusts  coating  volcanic  rocks. 

It  is  mined  with  other  copper  compounds  as  an  ore 
of  copper. 

122.  Apophyllite  (HzKCa^SiOsV^HsO)  is  found 


FIG.  79. — Apophyllite  Crystals. 

in  brilliant  prismatic  crystals  (Fig.  79),  with  a  square 
cross-section  and  in  granular  and  lamellar  masses. 

Its  crystals  have  one  very  perfect  cleavage,  and  the 
cleavage  surfaces  exhibit  a  distinct  pearly  luster.  On 
other  surfaces,  the  luster  is  glassy.  Its  color  is  white, 
gray  or  reddish  and  the  streak  colorless.  Its  hardness 
is  4.5-5  and  sp.gr.  2.3. 


DESCRIPTION  OF  MINERALS  121 

Before  the  blowpipe,  apophyllite  exfoliates  and 
fuses  easily  to  a  white,  blebby  enamel  and  imparts  a 
violet  color  to  the  flame.  In  the  closed  tube,  it  yields 
some  water  at  a  low  temperature  and  becomes  opaque. 
The  last  traces  of  water  are  lost  only  at  a  red  heat. 
Most  specimens  react  for  F.  The  mineral  dissolves  in 
HC1,  yielding  slimy  silica. 

Apophyllite  is  recognized  by  its  crystals,  its  pearly 
luster  on  cleavage  surfaces  and  in  most  instances  by 
the  reaction  for  F. 

ZEOLITES 

The  zeolites  comprise  a  group  of  minerals  that  are 
hydrous  silicates  of  Al  and  of  Ca,  Sr,  Ba,  Na  and  K. 
The  calcium  and  sodium  compounds  are  the  most 
common. 

Some  of  them  are  primary  minerals  which  resulted 
from  the  cooling  of  an  igneous  magma,  but  in  the  great 
majority  of  cases  they  are  secondary  products  that  have 
resulted  from  the  alteration  and  hydration  of  alkali- 
aluminium  silicates,  such  as  the  feldspars,  leucite, 
nephelite,  etc. 

They  are  nearly  always  found  in  veins  or  on  the 
walls  of  crevices  in  rocks  (especially  lavas),  where  they 
have  been  deposited  by  circulating  water. 

All  are  well  crystallized,  forming  Jiandsome  crystals 
which  in  some  cases  are  extremely  complicated.  They 
are  transparent  or  translucent,  and  are  usually  of  some 
light  shade  of  color.  Their  luster  is  usually  glassy 
and  their  streak  is  colorless. 

Before  the  blowpipe,  all  the  zeolites  fuse  with 
intumescence  or  bubbling,  and  all  give  water  in  the 
closed  tube.  They  are  comparatively  soft  (3.5-5.5) 
and  have  a  low  sp.gr. 


122  MINERALS  AND  BOCKS 

The  most  common  are  the  following  with  their 
compositions,  hardnesses  and  specific  gravities: 

Phillipsite  K2CaAl2(Si03)4-4£H2O  H.,  4  Sp.gr.,  2.2 

Harmotome  H2(Ba,K2)Al2(Si03)5-5H20  H.,  4.5  Sp.gr.,  2.5 

Stilbite  (Na2,Ca)Al2Si6Oi6  •  6H20  H.,  3-4  Sp.gr.,  2.2 

Laumontite  H4CaAl2Si4014  •  2H20  H.,  3-3.5  Sp.gr.,  2.35 

Scolecite  Ca(A10H)2(Si03)2  •  2H20  H.,  5-5.5  Sp.gr.,  2.3 

Chabazite  (Ca,Na2)Al2(Si03)4*  6H20  H.,  4.5  Sp.gr.,  2.1-2.16 

Analcite  NaAl(SiO,), •  H20  H.,  5-5.5  Sp.gr.,  2.2-2.3 

Natrolite,  Na2Al2Si3010 •  2H20  H.,  5-5.5  Sp.gr.,  2.2-2.5 

123.  Phillipsite  and  (124.)  Harmotome  are  dis- 
tinguished by  their  complicated  twinning  when  in 
crystals  (Fig.  80).  They  are,  however,  sometimes 


FIG.  80. — Harmotome  FIG.  81. — Sheaf-like  Group 

Crystal.  of  Stilbite  Crystals. 

found  in  radially  fibrous,  globular  aggregates.  Crys- 
tals of  harmotome  have  one  distinct  cleavage  and 
those  of  phillipsite,  two.  They  fuse  to  a  white  glass 
and  are  decomposed  by  HC1.  Phillipsite  and  har- 
motome are  distinguished  by  the  fact  that  the  solu- 
tion of  the  former  does  not  yield  a  precipitate  with 
H2S04,  while  that  of  the  latter  yields  a  white  precipi- 
tate of  BaS04. 

125.  Stilbite    occurs    in    sheaf-like    aggregates    of 
tabular  crystals  (Fig.  81),  in  radiating  bundles  and  in 


DESCRIPTION  OF  MINERALS 


123 


thin,  platy  prisms.  It  has  one  perfect  cleavage. 
Before  the  blowpipe  it  exfoliates,  swells  and  crinkles. 
It  is  decomposed  by  HC1. 

126.  Laumontite  occurs  in  prismatic  crystals  (Fig. 
82)    and   in   radial   fibers.     The    crystals 

have  two  perfect  cleavages.  The  luster 
on  these  surfaces  is  pearly.  Before  the 
blowpipe  the  mineral  swells  and  melts  to 
a  white  glass.  It  gelatinizes  in  HC1  and 
readily  yields  some  water  at  low  tempera- 
tures. A  red  heat,  however,  is  required  to 
drive  off  the  last  traces. 

127.  Scolecite  is  in  silky,  fibrous  and 
dense,  radiating  masses,  and  also  in  acic- 

ular  and  columnar  crystals  which  are  often  aggre- 
gated into  divergent  groups  (Fig.  83).  It  has  one 
perfect  cleavage.  Before  the  blowpipe,  it  crinkles  and 


FIG.  82. 

Laumontite 

Crystal. 


FIG.  83. — Group  of  Scolecite  Crystals. 

fuses  to  a  white  enamel.     In  the  closed  tube,  it  becomes 
opaque.     It  gelatinizes  with  acids. 

128.  Chabazite  occurs  in  rhombohedral  crystals 
which  have  a  cubical  habit  (Fig.  84).  It  occurs  also  in 
granular  aggregates.  It  has  a  distinct  cleavage, 


124  MINERALS  £ND  ROCKS 

parallel  to  the  rhombohedral  faces.  Before  the  blow- 
pipe, chabazite  swells  and  fuses  to  a  porous,  trans- 
lucent glass.  In  the  closed  tube,  it  loses  water  and 
cracks,  but  remains  clear.  It  is  decomposed  by 
HC1,  yielding  slimy  silica;  but  after  fusion,  it  is  in- 
soluble. It  is  distinguished  by  its  crystallization  and 
its  reaction  in  the  closed  tube. 

129.  Natrolite    occurs   in    acicular    crystals    (Fig. 
85)  which  are  often  arranged  in  radial  and  fibrous 


FIG.  84. — Chabazite  Crystals.  FIG.  85. — Natrolite  Crystal. 

aggregates  forming  tufts,  and  in  granular  and  dense 
masses.  It  is  usually  glassy  and  possesses  one  dis- 
tinct cleavage.  Before  the  blowpipe,  it  fuses  quietly 
to  a  colorless  glass,  coloring  the  flame  yellow. 

130.  Analcite  is  found  in  isometric  crystals  (Fig. 
86)   like  those  of  leucite  and  garnet   (Nos.  101,  88). 


FIG.  86. — Analcite  Crystals. 

It  possesses  a  very  imperfect  cleavage.  Before  the 
blowpipe,  the  mineral  fuses  to  a  colorless  glass,  impart- 
ing a  yellow  color  (Na)  to  the  flame.  In  the  closed 
tube,  it  gives  water,  but  retains  its  form  and  luster. 


DESCRIPTION  OF  MINERALS  125 

Its  powder  gelatinizes  with  HC1.  It  is  distinguished 
from  garnet  (No.  88)  by  its  much  inferior  hardness 
and  its  solubility  in  acid  and  from  leucite  (No.  101) 
by  the  presence  of  water,  its  easy  fusibility,  its  inferior 
hardness,  and  the  color  it  imparts  to  the  flame.  Be- 
sides occurring  like  other  zeolites,  analcite  also  occurs 
as  an  essential  component  of  some  lavas. 

TITANATES   AND    TITANO-SILICATES 

Titanates  are  salts  of  titanium  acids  analogous 
to  those  of  silicic  acid.  Normal  titanic  acid  is  H4Ti04. 
The  meta  acid  is  H4Ti04-H2O  =  H2Ti03.  Dititan- 
ates  are  salts  of  HaTisOs^^T^-^HsC^I^TisOs). 

131.  Titanite  or  sphene  (CaSiTi05)  may  be  re- 
garded as  a  dititanate  in  which  one  Ti  is  replaced  by 


FIG.  87.— Titanite  Crystals. 

one  Si.  It  occurs  in  crystals  of  various  habits,  some 
of  which  are  double  wedge-shaped  (Fig.  87);  others 
envelope-shaped;  some  prismatic,  and  others  tabular. 
They  have  a  prismatic  cleavage. 

The  mineral  is  usually  brown,  gray,  black  or 
white.  Its  streak  is  white,  and  its  luster  vitreous. 
It  is  translucent  or  opaque.  Its  hardness  is  5-5.5 
and  sp.gr.  3.5. 

Before  the  blowpipe,  sphene  fuses  to  a  dark  glass. 
With  beads,  some  specimens  exhibit  the  reactions  for 
manganese  (p.  159)  and  all  show  those  characteristic 


126  MINEEALS  AND  EOCKS 

of  titanium.  All  varieties  are  sufficiently  soluble  in 
HC1  to  give  the  violet-colored  solution  when  treated 
with  tin.  The  mineral  is  completely  decomposed 
by  H2S04.  Sphene  is  distinguished  from  stauro- 
lite  (No.  93)  and  garnet  (No.  88)  by  its  crystalliza- 
tion and  softness;  from  sphalerite  (No.  10)  by  its 
greater  hardness  and  from  other  similarly  colored 
minerals  by  the  reactions  for  Ti  (p.  164). 

The  mineral  is  a  widespread  constituent  of 
igneous  rocks,  of  many  schists  and  of  metamorphosed 
limestones.  It  occurs  also  as  crystals  on  the  walls 
of  cracks  and  cavities  in  acid  granular  rocks. 

132.  Ilmenite  (FeTiOs),  the  iron  metatitanate, 
looks  very  much  like  hematite  (No.  38)  when  in 
crystals  (Fig.  88)  and  very  much  like 
magnetite  (No.  47)  when  massive. 
The  mineral  is  rarely  found  in  crystals. 
It  is  usually  in  homogeneous  masses,  in 
granular  aggregates,  in  thin  plates  and 
in  sand  grains. 

"Fir1    SS 

Ilmenite  Crystal.         It  is  black  and  opaque  and  its  streak 
is  black  or  brownish-red.    It  has  a  sub- 
metallic  luster,  a  hardness  c  f  5-6  and  a  sp.gr.  of  4.5-5. 
It  is  slightly  magnetic. 

Before  the  blowpipe,  it  is  nearly  infusible.  It 
gives  the  reactions  for  iron  (p.  141)  with  the  beads. 
When  the  microcosmic  salt  bead,  which  is  brownish- 
red  in  the  reducing  flame,  is  heated  with  a  scrap  of 
tin  on  charcoal,  it  changes  to  a  violet-red  color.  The 
powder  of  ilmenite  is  slowly  dissolved  by  hot  HC1 
to  a  yellow  solution,  which,  if  filtered  and  boiled  with 
the  addition  of  tin,  changes  to  blue,  indicating  tita- 
nium. 


DESCRIPTION  OF  MINERALS  127 

Ilmenite  is  distinguished  from  hematite  by  its 
streak,  from  magnetite  by  its  lack  of  strong  magnet- 
ism, and  from  almost  all  other  heavy  black  minerals 
by  its  reaction  for  titanium  (p.  164). 

It  is  found  as  a  constituent  of  many  basic  igneous 
rocks,  as  veins  cutting  them,  and  also  as  great  masses 
near  their  contacts  with  other  rocks.  In  a  few  places, 
it  forms  the  principal  component  of  sand. 

Attempts  have  been  made  to  utilize  ilmenite  as 
an  ore  of  iron,  but  on  account  of  its  large  content  of 
titanium,  no  satisfactory  means  of  smelting  it  on  a 
commercial  scale  has  been  successful.  At  present, 
therefore,  it  has  little  value. 


Ill 


DETERMINATION  OF  MINERALS  WITH  THE  AID 
OF  THE  BLOWPIPE 

THE  recognition  of  a  mineral  by  mere  inspection 
is  often  difficult,  and  is  frequently  impossible  if  crys- 
tals are  not  available.     In  this  case,  recourse  is  had 
to  means  that  will  aid  in  determining  its  chemical 
composition,  or  at  least  the  nature  of  one  or   more 
of  its  constituents.      The  most  convenient  methods 
made  use  of  for  this  purpose  are  those  based  on  del- 
icate and  characteristic  reactions  that  take  place  with 
solid   reagents    at    high    temperatures.      The    results 
are   only   qualitative,   but   when   combined  with   the 
study   of    the    physical   properties   of   the   substance 
tested    they   are    sufficiently  definite   to   enable    one 
to  recognize  its  nature.     In  a  few  instances,   liquid 
reagents  must  be  employed  to  give  decisive  results,  but 
th^y  are  few  and  easily  obtained.     Analysis  at  high 
temperatures  is  known  as  blowpipe  analysis,  because 
the  required  heat  is  obtained  by  the  use  of  the  blowpipe. 
The  Blowpipe. — The  blowpipe,  in  its  simplest  form, 
is  a  tube  with  a  small  outlet  through  which  a  current 
of  air  may  be  directed  through  a  flame  upon  a  small 
particle  of  substance.     A  practical  instrument  consists 
of   a   mouthpiece,    a   tube,    an  air-chamber  to  catch 
moisture,  a  side  tube  and  a  tip  pierced  by  a  tiny  hole 
(Fig.  89).     The  tip  is  placed  in  the  flame  of  a  Bunsen 

128 


DETERMINATION  OF  MINERALS 


129 


burner,  an  alcohol  lamp  or  some  other  source  of  flame, 
and  a  current  of  air  is  blown  through  it  by  placing  the 
mouthpiece  to  the  lips,  breathing  full,  and  allowing  the 
contraction  of  the  cheeks  to  force  the  air  from  the 
mouth.  Other  forms  of  blowpipe  are  advocated  for 
special  purposes.  Fre- 
quently, the  side  tube  is 
curved  in  such  a  way 
that  the  air  passing 
through  is  heated  before 
it  issues  from  the  tip 
and  a  hotter  flame  is 
produced  than  is  pos- 
sible with  the  simpler 
instrument. 

Since  it  is  often  de- 
sirable to  have  both 
hands  free  to  manipulate 
the  assay,  a  blower  is 
sometimes  attached  to 
the  blowpipe. 

Source  of  Heat— 
The  best  source  of  flame 
for  general  use  with  the 
blowpipe  is  the  Bunsen 
burner  supplied  by  or- 
dinary gas,  and  furnished 
with  a  tip  which  is  flat- 
tened at  the  upper  end  and  cut  off  obliquely.  The 
blowpipe  is  supported  on  the  upper  end  of  this  tip 
and  pointed  downward  parallel  with  it.  Thus,  the 
flame  is  blown  down  upon  the  assay. 

Since,    however,    illuminating   gas   often   contains 


FIG.  89. — Simple  Blowpipe. 


130  MINERALS  AND  ROCKS 

noticeable  traces  of  sulphur,  for  the  detection  of  this 
substance  it  is  often  advisable  to  substitute  an  alcohol 
lamp  for  the  gas  burner.  With  the  alcohol  should  be 
mixed  a  little  turpentine  in  the  proportion  of  one  part 
of  the  latter  to  twelve  of  the  former  to  increase  the  re- 
ducing power  of  the  flame. 

Supports. — The  principal  supports  used  to  hold  the 
material  under  investigation — the  assay — are  charcoal, 
platinum,  and  glass.  Sheets  of  aluminium,  plaster 
slabs  and  unglazed  porcelain  are  also  sometimes  em- 
ployed, but  for  most  purposes  the  first  three  are  entirely 
adequate. 

Charcoal. — Charcoal  is  used  in  reduction  tests  and 
in  the  study  of  sublimates.  It  should  have  a  flat 
surface  and  should  be  well  burned. 

Platinum. — Platinum  is  used  principally  in  the  form 
of  wire  and  foil.  The  wire  should  be  of  about  the  thick- 
ness of  coarse  horsehair  (.4  mm.),  and  should  be  fused 
into  a  3-inch  long  glass  tube  to  serve  as  a  handle. 
It  is  employed  mainly  in  the  production  of  colored 
glasses  or  beads.  The  foil  should  be  thin.  When 
about  to  be  used,  it  should  be  bent  into  a  shallow  cup 
in  which  mixtures  may  be  fused. 

Glass. — Glass  is  used  in  the  form  of  tubes.  These 
should  be  of  a  hard  glass  about  90  mm.  long  and  6  mm. 
inside  diameter.  When  closed  at  one  end,  they  serve 
to  hold  substances  which  are  to  be  heated  to  a  high 
temperature  in  the  study  of  their  volatile  constituents. 
Tubes  open  at  both  ends  are  employed  to  study  the 
effect  of  roasting  the  assay  in  a  current  of  air. 

Other  Apparatus. — Other  pieces  of  apparatus  de- 
sirable for  satisfactory  blowpipe  work  are:  a  magnet, 
a  magnifier,  a  pair  of  forceps,  a  small  hammer,  an  anvil, 


DETERMINATION  OF  MINERALS 


131 


a  pair  of  cutting  pincers,  a  piece  of  blue  glass  or  a 
screen  composed  of  strips  of  celluloid  colored  different 
shades  of  blue,  or  a  hollow  glass  prism  filled  with 
indigo  solution. 

Reagents. — Since  blowpipe  tests  are  made  on  minute 
quantities  of  material,  it  is  necessary  that  all  reagents 
used  be  as  pure  as  possible.  Those  most  frequently 
employed  are:  borax,  Na2B407-10H2O;  microcosmic 
salt,  or  salt  of  phosphorus,  NH4NaHPO4-4H20;  fused 
sodium  carbonate,  Na2CO3;  acid  potassium  sulphate, 
HKSO4;  niter, KN03',  cobalt  nitrate,  Co(N03)2-6H2O, 
in  solution;  copper  oxide,  CuO;  magnesium  ribbon, 
Mg;  granulated  zinc,  Zn;  sulphuric  acid,  H2S04;  hydro- 
chloric acid,  HC1,  and  blue  litmus  and  turmeric  papers. 
Other  reagents  are  employed  in  special  tests,  but 
those  mentioned  above  are  used  generally. 

The  Blowpipe  Flame. — The  blowpipe  flame  is 
used  not  only  for  producing  a  high  tem- 
perature, but  also  to  produce  oxidizing 
and  reducing  effects.  The  oxidizing 
flame  aids  in  adding  oxygen  to  the  sub- 
stance heated  and  the  reducing  flame 
abstracts  it. 

A  luminous  flame,  such  as  is  pro- 
duced by  a  candle  or  a  Bunsen  burner, 
with  the  airholes  at  the  foot  of  the 
tube  closed,  consists  of  (c)  an  inner, 
non-luminous  cone  (Fig.  90)  containing 
unignited  gas,  (6)  a  luminous  envelope 
surrounding  this,  in  which  there  is 
partial  combustion  of  the  gas  passing 
out  from  the  non-luminous  cone,  and  an  outer  pur- 
plish mantle. 


FIG.  90. 
Candle  Flame. 


132  MINERALS  AND  ROCKS 

Because  protected  from  the  air  by  the  outer  mantle, 
the  gas  in  the  luminous  inner  cone  is  not  entirely  con- 
sumed. The  available  oxygen  combines  with  the 
easily  combustible  hydrogen,  while  the  carbon  of  the 
gas  is  separated  in  extremely  fine  particles.  These 
are  at  a  high  temperature  and  are,  therefore,  incan- 
descent. In  this  condition,  carbon  is  an  active  reducing 
agent,  combining  with  oxygen  readily,  abstracting  it 
for  this  purpose  from  any  oxygen-bearing  compound 
with  which  it  is  brought  in  contact.  Consequently, 


FIG.  91. — Reducing  Flame. 

this  portion  of  the  flame  exerts  a  reducing  action  upon 
anything  within  its  sphere.  In  the  outer  mantle, 
there  is  an  abundance  of  oxygen.  This  combines  with 
the  carbon  particles  as  they  pass  out  from  the  luminous 
envelope,  forming,  at  first,  carbon  monoxide,  CO. 
This  unites  with  more  oxygen  forming  carbon  dioxide, 
C02,  and  giving  a  blue  flame.  Since  the  temperature 
in  this  portion  of  the  flame  is  very  high  and  there  is  an 
abundance  of  oxygen  present,  substances  subjected 
to  its  action  are  oxidized. 

The  use  of  the  blowpipe  accentuates  the  effect 
of  the  different  portions  of  the  flame  and  serves  to 
direct  it  upon  the  particle  to  be  tested. 


DETERMINATION  OF  MINERALS  133 

To  produce  the  reducing  flame  (R.F.),  the  blow- 
pipe jet  is  placed  at  the  edge  of  the  burner  flame  near 
its  base,  and  a  gentle  current  of  air  is  blown  (Fig.  91). 
This  deflects  the  flame  without  mixing  too  much 
oxygen  with  it — and  it  remains  luminous.  Its  most 
energetic  part  is  near  the  end  of  the  luminous  cone  (a). 

The  oxidizing  flame  (O.F.)  is  produced  by  passing 
the  tip  of  the  blowpipe  into  the  flame  a  short  distance 
(Fig.  92)  and  blowpiping  strongly,  but  steadily. 
A  sharp-pointed,  non-luminous  flame  results,  with  an 


FIG.  92. — Oxidizing  Flame. 

inner  blue  cone.     The  most  effective  oxidizing  area 
is  just  beyond  the  tip  of  the  blue  cone. 

Before  attempting  to  use  the  blowpipe  for  pro- 
ducing oxidizing  and  reducing  effects,  the  two  flames 
should  be  practiced  with  until  they  can  be  manipu- 
lated with  certainty.  The  reducing  flame  is  the  most 
difficult  to  use  successfully.  It  must  be  maintained 
unchanged  for  some  time  and  the  assay  must  be  com- 
pletely enveloped  in  it  to  secure  satisfactory  results. 
Otherwise,  oxidation  may  ensue.  In  order  to  test 
one's  ability  to  reduce  with  the  blowpipe  flame,  a  little 
borax  should  be  melted  in  a  small  loop  made  at  the  end 
of  a  platinum  wire.  It  will  form  a  colorless  glass. 
Into  this  should  be  introduced  a  tiny  grain  of  some 


134  MINERALS  AND  ROCKS 

manganese  compound.  If  the  borax  with  the  added 
manganese  is  heated  in  the  oxidizing  flame,  an  ame- 
thyst-colored glass  will  result.  This,  if  heated  in  the 
reducing  flame,  will  again  become  colorless,  but 
the  color  will  return  if  the  assay  is  touched  by  the 
oxidizing  flame.  When  the  color  can  be  made  to  dis- 
appear and  reappear  at  will,  the  proper  amount  of 
skill  for  the  manipulation  of  the  flames  will  have  been 
attained. 

Use  of  the  Closed  Tube. — The  closed  glass  tube 
is  used  to  discover  whether  a  substance  contains 
water  or  not,  to  detect  its  volatile  constituents,  and  to 
discover  the  nature  of  its  decomposition  products. 
It  is  also  employed  in  the  observation  of  certain  other 
characteristic  changes  in  a  substance  produced  by 
heating  to  a  high  temperature. 

The  material  to  be  tested  is  powdered  and  slid  into 
the  tube  with  the  help  of  a  little,  narrow  paper  trough, 
which  is  long  enough  to  reach  nearly  to  its  bottom. 
The  tube  is  then  tapped  to  settle  the  material  and  the 
end  containing  the  assay  is  heated,  at  first  gently, 
later  more  vigorously,  even  to  redness,  either  in  the 
burner  flame  or  in  the  flame  produced  by  the  blow- 
pipe. 

WATEK  is  indicated  by  the  condensation  of  little 
drops  on  the  upper,  cooler  portion  of  the  tube.  If  the 
water,  when  tested  with  litmus  paper,  reacts  acid, 
a  volatile  acid  (H2S04,  HC1,  HN03  or  HF)  is  indicated. 
If  it  reacts  alkaline,  ammonia  has  been  evolved. 

GASES. — The  character  of  the  gases  evolved  is  best 
recognized  by  their  color  and  odor. 

(a)  Hydrogen  sulphide  (H2S)  is  recognized  by  its 
odor.  It  indicates  a  sulphide  containing  water. 


DETERMINATION  OF  MINERALS  135 

(b)  Nitrogen  peroxide  (N204)  is  recognized  by  its 
reddish-brown  fumes  and  its  characteristic  odor.     It 
indicates  a  nitrate  or  a  nitrite.    In  the  case  of  HNOs, 
the  reaction  is  2HN03  =  O+H20+2N02. 

(c)  Hydrofluoric  acid  (HF)  attacks  the  glass  of  the 
tube  and  etches  it.     Its  presence  in  the  assay  indicates 
a  fluoride. 

SUBLIMATES  or  coatings  may  be  deposited  in  the 
cooler  portion  of  the  tube. 

(a)  If  white,  they  may  indicate  ammonia  salts, 
antimony  trioxide,  arsenic  trioxide  or  tellurium  di- 
oxide. 

(6)  If  gray  or  black,  they  indicate  arsenic,  mercury 
or  tellurium. 

(c)  If  black,  while  hot,  and  reddish-brown,  when 
cold,  antimony  sulphide;  and  if  reddish-brown,  while 
hot,  and  reddish-yellow,  when  cold,  arsenic  sulphide. 

CHANGES  OF  COLOR  are  very  characteristic  for 
certain  substances,  the  following  being  of  greatest 
importance : 

(a)  From  white  to  yellow  and  to  white  again  on 
cooling:  zinc  oxide. 

(6)  From  white  to  brownish-red  and  back  to  yellow: 
lead  oxide. 

(c)  From  white  to  orange-yellow  and  back  to  pale 
yellow  when  again  cold:   bismuth  oxide. 

(d)  From  red  to  black  and  red  again  when  cold: 
mercuric   and   ferric   oxides.     The  mercury  oxide   is 
volatile. 

Use  of  the  Open  Tube. — The  open  tube  is  used  when 
it  is  desired  to  treat  the  assay  with  a  current  of  hot 
oxygen.  It  is  charged  in  the  same  manner  as  the 
closed  tube,  the  assay  being  placed  about  12  mm. 


136  MINERALS  AND  ROCKS 

from  the  end.  The  tube  is  then  held  in  the  forceps 
over  the  flame,  care  being  taken  to  incline  it  slightly 
for  the  purpose  of  producing  an  upward  current. 
By  this  means,  the  following  substances  are  easily 
detected : 

Sulphur  is  detected  by  the  choking  odor  of  SO 2. 

Arsenic  yields  a  white  volatile  sublimate,  which 
disappears  upon  heating. 

Antimony  gives  white  fumes  which  may  partly 
condense  on  the  cooler  portion  of  the  tube  as  a  white 
sublimate  and  partly  escape  from  its  end.  The  sub- 
limate is  only  slightly  volatile. 

Mercury  yields  globules  of  mercury. 

Tellurium  yields  a  white  sublimate,  which,  when 
heated,  fuses  to  colorless  drops. 

Selenium  gives  a  sublimate  which  is  white  or  steel- 
gray  near  the  assay  (SeC>2)  and  red  at  a  greater  dis- 
tance (Se02  and  Se).  The  odor  of  the  volatile  metal 
is  exceedingly  disagreeable.  If  the  tube  is  allowed  to 
discharge  through  the  flame,  it  will  produce  a  blue 
color. 

The  Use  of  the  Charcoal. — A  shallow  depression 
is  made  near  one  end  of  a  piece  of  charcoal,  the  pow- 
dered assay  placed  in  this,  and  the  blowpipe  flame 
played  upon  it,  while  the  charcoal  is  held  in  a  tilted 
position  by  the  left  hand.  If  the  assay  decrepitates 
when  heated,  it  should  be  moistened  with  a  drop  of 
water.  The  principal  phenomena  to  be  noted  are: 
volatilization,  fusibility,  decrepitation,  deflagration, 
odor,  reduction  and  the  production  of  sublimates. 

Volatilization. — The  substance  vaporizes  and  dis- 
appears. 

Fusibility. — The  substance  melts  entirely  or  par- 


DETERMINATION  OF  MINERALS  137 

tially  in  the  different  parts  of  the  flame,  some  sub- 
stances fusing  easily  and  others  only  with  great 
difficulty. 

Decrepitation. — The  substance  flies  to  pieces  when 
heat  is  applied,  indicating  decomposition  or  the  pres- 
ence of  water,  or  included  gases. 

Deflagration. — The  substance  suddenly  burns  with 
little  explosions  characteristic  of  nitrates. 

Reduction  and  Sublimation. — When  heated  on  char- 
coal with  the  R.F.,  some  substances  may  easily  be 
reduced  to  the  metallic  state,  others  are  reduced 
with  difficulty.  Thus,  2PbO+C  =  Pb2+C02.  Reduc- 
tion takes  place  most  readily  if  the  assay  is  powdered 
and  mixed  with  about  four  times  its  volume  of  dry 
sodium  carbonate  (Na2C03) .  Thus : 

2PbS+2Na2C03+C  =  2Na2S+Pb2+3CO2. 

In  cases  of  great  difficulty,  a  little  potassium  cyanide  l 
(KCN)  or  borax  (Na2B407-10H20)  added  to  the 
mixture  will  frequently  hasten  the  result.  In  any  case, 
the  heat  must  be  applied  until  nearly  all  the  assay 
sinks  into  the  charcoal. 

When  sufficiently  heated,  some  substances  yield  a 
globule  of  metal,  others  are  completely  volatilized, 
others  yield  fumes,  produced  by  the  oxidation  of 
portions  of  the  assay,  while  yet  others  are  partly  re- 
duced to  a  globule  of  metal  and  partly  volatilized. 
Thus,  during  the  reduction  of  PbS,  some  of  the  lead 
may  be  oxidized  according  to  the  reaction: 

PbS+Na2C03  =  Na2S+PbO+CO2, 

1  Potassium  cyanide  must  always  be  used  with  care,  as  it  is  a  deadly 
poison,  even  in  minute  quantities. 


138  MINERALS  AND  ROCKS 

and  a  portion  of  the  oxide  may  settle  on  the  coal. 
When  fumes  are  produced,  they  are  deposited  upon  the 
cooler  portions  of  the  charcoal  in  the  form  of  sub- 
limates which  possess  characteristic  properties. 

Gold,  silver,  and  copper  compounds  yield  globules 
of  metal  without  sublimates.  The  metals  are  sep- 
arated for  examination  by  cutting  out  the  charcoal 
beneath  the  assay,  and  crushing  the  mass  with  water 
in  a  small  mortar.  Upon  pouring  off  the  water,  the 
metal  remains  as  spangles,  grains  or  powder.  The 
silver  is  recognized  by  its  color  and  by  the  fact  that 
its  solution  in  nitric  acid  yields  a  white  precipitate 
upon  the  addition  of  a  drop  or  two  of  hydrochloric 
acid.  Copper  and  gold  have  nearly  the  same  color, 
but  copper  dissolves  in  nitric  acid  while  gold  is  in- 
soluble. Addition  of  an  excess  of  ammonia  to  the 
solution  of  copper  gives  a  characteristic,  deep  blue  color. 

Iron,  nickel,  and  cobalt  give  gray  infusible  powders 
which  are  magnetic,  but  yield  no  sublimates. 

Molybdenum,  tungsten,  and  some  of  the  rarer 
metals  give  gray  powders  that  are  non-magnetic  and 
no  sublimates. 

Antimony  yields  copious  white  fumes,  forming  a 
volatile  white  sublimate  (Sb2Os),  which  becomes 
black  when  touched  with  the  R.F.  When  touched 
by  the  tip  of  the  O.F.,  it  will  volatilize  and  color 
the  flame  yellowish-green.  The  metallic  bead,  when 
dropped  upon  a  sheet  of  glazed  paper,  breaks  into 
a  number  of  smaller  ones. 

Arsenic  volatilizes  completely  and  consequently 
yields  no  globule  of  metal.  It  gives  abundant  white 
fumes  which  form  a  white  sublimate  and  have  a  garlic 
odor.  The  flame  at  the  same  time  is  colored  blue. 


DETERMINATION  OF  MINERALS  139 

Bismuth  yields  a  reddish-white,  brittle  globule  and 
an  orange-yellow  sublimate  which  becomes  lemon- 
yellow  when  cold. 

Cadmium  gives  brown  fumes  in  the  O.F.  and 
yields  a  reddish-brown  sublimate,  while  the  flame  is 
colored  dark  green. 

Lead  yields  a  gray  malleable  bead,  and  incrusts 
the  charcoal  with  a  lemon-yellow  sublimate  near  the 
assay.  The  flame  at  the  same  time  is  colored  blue. 
The  yellow  incrustation  is  composed  of  lead  oxide. 

Molybdenum  gives  a  crystalline  incrustation  which 
is  yellow  when  hot  and  white  when  cold.  When 
touched  by  the  O.F.  it  becomes  dark  blue,  and  when 
heated  for  a  longer  time  dark  copper  red.  The 
blue  incrustation  may  be  molybdenum  molybdate 
(MoMo04)  and  the  red  one,  molybdenum  dioxide 
(Mo02), 

Selenium  yields  brown  fumes,  but  the  sublimate 
which  is  near  the  assay  is  gray.  When  heated  with 
the  reducing  flame,  it  disappears  and  the  charistic 
bad  odor  is  evolved.  The  flame  becomes  blue. 

Tellurium  coats  the  charcoal  with  a  white  sub- 
limate bordered  by  dark  yellow.  The  coating  dis- 
appears in  the  R.F.,  which  acquires  a  green  color. 

Tin  gives  a  white  globule  which  is  malleable  and 
a  yellowish-white  coating,  turning  white  upon  cooling. 
When  moistened  with  a  drop  of  Co(N03)2  solution  and 
heated  in  the  O.F.,  its  color  changes  to  blue-green. 

Zinc  burns  in  the  O.F.  with  a  bluish-white  color 
and  evolves  thick  white  fumes  which  condense  as  a 
yellowish  sublimate.  This  becomes  white  on  cooling, 
and,  when  moistened  with  a  drop  of  cobalt  nitrate 
and  again  heated,  it  turns  grass-green  (compare  tin). 


140  MINERALS  AND  ROCKS 

Other  metals  also  give  characteristic  reactions  on 
charcoal,  but  the  above  are  the  most  important. 

Use  of  the  Beads. — The  beads  are  used  for  the 
detection  of  metals  that  produce  characteristic,  colored 
compounds  when  fused  with  borax  or  microcosmic 
salt  or  some  other  reagent.  A  piece  of  platinum  wire 
fused  into  a  glass  rod  serves  as  a  support.  The  end 
of  the  wire  is  bent  into  a  little  loop.  This  is  moistened 
and  plunged  into  powdered  borax,  microcosmic  salt 
or  other  reagent  and  then  heated  carefully  until  the 
adhering  material  is  fused  to  a  clear  glass.  New 
material  is  added  by  dipping  the  loop  again  and  again 
into  the  powdered  salt  and  heating  until  the  globules 
of  glass  are  large  enough  to  fill  it  completely.  A 
tiny  portion  of  the  material  to  be  tested  is  taken  up 
by  heating  the  bead  and  pressing  it  while  still  soft 
upon  a  tiny  bit  of  the  powdered  assay,  which  has 
been  placed  in  a  clean  watch-glass.  The  bead  con- 
taining the  substance  is  then  heated  with  the  O.F.  and 
afterward  with  the  R.F.  and  the  phenomena  resulting 
are  carefully  observed.  If  the  reduction  is  difficult,  a 
little  stannous  oxide  or  chloride  will  hasten  it.  If  the 
bead  becomes  opaque  because  saturated  with  the 
assay,  a  portion  is  jerked  off  while  it  is  hot  and  it  is 
built  up  again  by  the  addition  of  more  of  the  reagent. 

In  some  cases,  compounds  other  than  the  oxides 
do  not  yield  the  characteristic  beads  of  the  metallic 
oxides.  Therefore,  it  is  safer  in  all  cases  when  testing 
by  the  bead  reaction,  to  first  roast  the  substance  by 
gently  heating  on  charcoal  with  the  O.F.  to  drive  off 
its  volatile  constituents. 

The  colors  of  the  most  characteristic  beads  of 
metallic  oxides  are  tabulated  on  the  opposite  page: 


DETERMINATION  OF  MINERALS 

COLORS  OF  BORAX  BEADS 


141 


Oxidizing  Flame. 

•    Reducing  Flame. 

Hot. 

Cold. 

Hot. 

Cold. 

Yellow  or  red 

Grass-green 

Chromium 

Green 

Emerald-green 

Blue 

Blue 

Cobalt 

Blue 

Blue 

Green 

Blue 

Copper 

Colorless 

Reddish-brown, 

opaque 

Colorless 

Colorless 

Didymium 

Rose 

Rose 

Yellow  or  red 

Colorless  or 

Iron 

Bottle-green 

Bottle-green 

yellow 

Violet 

Reddish-violet 

Manganese 

Colorless 

Colorless 

Yellow  or  red 

Colorless  to 

Molybdenum 

Brown 

Opaque-brown 

opalescent 

Violet 

Reddish-brown 

Nickel 

Gray 

Gray 

Colorless 

Colorless 

Columbium 

Colorless  or 

Colorless  or 

grav 

gray 

Colorless  or 

Colorless 

Titanium 

Yellow  or 

Yellow  or 

yellow 

brown 

brown 

Colorless  or 

Colorless 

Tungsten 

Yellow 

Yellow-brown 

yellow 

Yellow  or  red 

Colorless  or 

Uranium 

Pale  green 

Pale    green   to 

yellow 

nearly  color- 

less 

Yellow 

Green-yellow, 

Vanadium 

Brownish-green 

Emerald-green 

or  nearly 

colorless 

COLORS  OF  MICROCOSMIC  SALT  BEADS 


Oxidizing  Flame. 

Reducing  Flame. 

Hot. 

Cold. 

Hot. 

Cold. 

Reddish-green 

Emerald-green 

Chromium        !  Reddish-green 

Emerald-green 

Blue 

Blue 

Cobalt 

Blue 

Blue 

Green 

Blue 

Copper 

Dirty  green 

Green,  or 

opaque-red 

Colorless 

Colorless 

Didymium 

Colorless 

Blue 

Yellow  or  red 

Colorless,  yel- 

Iron 

Yellow  or  red 

Nearly  colorless 

low  or  brown 

Violet 

Violet 

Manganese 

Colorless 

Colorless 

Green 

Faint  yellow- 

Molybdenum 

Dirty  green 

Green 

ish-green 

Reddish  to 

Yellowish  to 

Nickel 

Reddish 

Yellowish  to 

brown 

reddish 

reddish-yellow 

Colorless 

Colorless 

Columbium 

Blue  or  brown 

Blue  or  brown 

Skeleton 

Skeleton 

Silica 

Skeleton 

Skeleton 

Colorless 

Colorless 

Titanium 

Yellow 

Violet 

Colorless 

Colorless 

Tungsten 

Dirty  green-blue 

Blue 

Yellow 

Yellow-green 

Uranium 

Dirty  green 

Bright  green 

to  colorless 

Dark  yellow 

Light  yellow 

Vanadium 

Brownish-green 

IE  merald-green 

to  colorless 

Cobalt  is  the  only  metal  which  produces  the  same 
colored  bead  under  all  conditions.  This  is  a  beautiful 
blue  bead.  Other  oxides  give  blue  beads  under  some 


142  MINERALS  AND  BOCKS 

one  or  more  conditions,  but  under  other  conditions 
their  beads  have  other  colors. 

The  cold  bead  of  chromium  oxide  is  always  green 
and  the  oxidized  bead  of  manganese  is  always  violet. 

Flame  Coloration. — Many  substances  impart  a 
distinct  color  to  the  non-luminous  flame  of  the  burner 
or  the  blowpipe.  Frequently,  these  colors  are  best 
seen  after  the  substance  in  powdered  form  has  been 
moistened  with  hydrochloric  acid,  as  the  chlorides  are 
usually  more  volatile  than  other  compounds.  In 
the  case  of  silicates,  it  is  often  advisable  to  mix  the 
powdered  assay  with  an  equal  volume  of  powdered 
gypsum.  In  testing  for  flame  coloration  a  very  small 
particle  of  the  substance,  or  its  moistened  powder, 
or  of  the  mixture  of  the  substance  and  gypsum  is 
held  in  the  flame  by  the  aid  of  the  platinum  loop  which 
has  been  cleaned  by  dipping  into  HC1,  and  heated 
repeatedly  until  it  no  longer  colors  the  flame. 

When  several  different  flame-coloring  elements 
are  present  in  the  assay,  the  stronger  color  may  mask 
the  fainter  one,  and,  therefore,  some  means  must  be 
made  use  of  to  shut  off  the  brighter  color,  while  allow- 
ing the  fainter  one  to  persist.  This  is  usually  accom- 
plished by  viewing  the  flame  through  some  medium 
(a  screen)  that  is  transparent  to  the  faint  rays  and 
opaque  to  the  brighter  ones.  In  other  cases,  two 
flames  which  are  really  different  in  color  appear  of 
nearly  the  same  tint  to  the  unaided  eye.  In  this 
case,  the  screen  is  again  used  to  cut  off  certain  rays 
that  are  common  to  the  two  colors,  when  the  remaining 
rays  may  be  different  enough  to  be  distinguishable. 
The  screens  most  frequently  used  for  this  purpose  are 
pieces  of  colored  glass,  which  are  held  close  to  the  eye. 


DETEEMINATION  OF  MINERALS  143 

Red  glass  absorbs  all  but  red  rays.  Blue  glass  stops 
certain  red  and  green  rays  and  all  the  yellow  ones. 
Great  difficulty  is  sometimes  experienced  in  securing 
glass  exhibiting  pure  colors,  so  that  in  most  cases  it 
is  more  convenient  to  use  transparent  celluloid  films 
that  have  been  manufactured  expressly  for  the  exami- 
nation of  colored  flames.  These  films  are  given  the 
tints  that  are  most  useful  for  the  purpose  desired 
Care  must  be  taken  in  using  them,  however,  since 
celluloid  is  highly  inflammable. 

For  more  accurate  work  the  spectroscope  is  often 
employed.  The  use  of  this  depends  upon  the  fact  that 
each  substance,  when  in  the  form  of  gas,  emits  light 
composed  of  one  or  more  rays  of  definite  wave  lengths, 
and  the  spectroscope  separates  these  so  that  each  may 
be  identified. 

The  most  characteristic  colors  imparted  to  the  blow- 
pipe flame  are: 

Red  by  lithium,  strontium,  and  calcium.  Sodium 
salts  obscure  the  lithium  flame  and  barium  salts  the 
strontium  and  calcium  flames. 

Yellow  by  sodium. 

Green  by  most  copper  compounds,  thallium,  barium, 
antimony,  phosphoric  acid,  boric  acid,  molybdic  acid, 
and  nitric  acid.  The  flame  of  phosphoric  acid  is 
bluish-green,  the  flames  of  boric  acid  and  barium  are 
yellow-green,  and  those  of  molybdic  acid  and  anti- 
mony are  very  faint.  The  copper  and  thallium 
flames  are  vivid  greens.  The  nitric  acid  flame 
coloration  is  bronze-green  and  it  exists  as  a  flash 
only. 

Blue  by  copper  chloride,  copper  bromide,  selen- 
ium, arsenic  and  lead.  The  arsenic  flame  is  faint. 


144  MINERALS  AND  ROCKS 

The   selenium   and   the   copper   chloride   flames   are 
brilliant  azure-blue. 

Violet  by  potassium,  caesium  and  rubidium.  So- 
dium and  lithium  salts  obscure  the  reaction. 

Detection  of  Certain  Elements  in  the  Presence  of 
Others. — In  many  cases,  as  has  been  stated,  the  color 
imparted  to  the  flame  by  one  substance  entirely  ob- 
scures that  given  it  by  another  when  the  two  are  pres- 
ent in  the  same  compound.  Thus,  the  faint  violet 
color  of  the  potassium  flame  is  obscured  by  the  strong 
yellow  of  sodium  and  the  brilliant  red  of  lithium. 
When  this  is  the  case,  the  light  is  viewed  through  the 
proper  screens  and  the  different  rays  in  this  manner 
are  differentiated.  Since  the  flame  tests  afford  the 
readiest  means  of  detecting  the  alkalies  and  alkaline 
earths,  considerable  attention  has  been  devoted  to 
means  of  differentiating  their  flame  colors.  Among 
the  methods  proposed  for  this  purpose  is  that  based 
upon  the  use  of  blue  and  green  glass  screens. 

Detection  of  the  Alkalies  and  the  Alkaline  Earths. 
-The  potassium  flame  is  reddish-violet  through  blue 
glass,  while  the  sodium  flame  is  invisible  or  is  blue; 
hence,  the  potassium  flame  is  detected  in  the  presence 
of  sodium  by  viewing  the  mixed  flame  through  a  blue 
screen.  Lithium  is  also  detected  in  the  presence  of 
sodium  with  the  aid  of  blue  glass,  since  the  lithium 
flame  is  violet-red  when  viewed  through  a  blue  screen. 
Since  the  flame  colors  of  Li  and  K  are  so  nearly  alike 
when  viewed  through  a  blue  screen,  they  cannot  easily 
be  distinguished.  When  viewed  through  a  green 
screen,  however,  the  Li  flame  is  nearly  invisible, 
while  that  of  K  is  bluish-green.  Through  the  green 
screen  the  Na  flame  appears  orange. 


DETERMINATION  OF  MINERALS 


145 


If  search  is  to  be  made  for  the  alkaline  earths, 
the  assay  is  repeatedly  moistened  with  sulphuric 
acid  and  placed  in  the  hottest  portion  of  the  flame. 
After  the  alkalies  are  driven  off,  the  flame  will  become 
yellowish-green,  if  barium  is  present;  through  green 
glass  it  will  appear  bluish-green.  The  assay  is  then 
repeatedly  moistened  with  pure  hydrochloric  acid  and 
again  brought,  while  still  moist,  into  the  hottest  por- 
tion of  the  flame.  A  red  coloration,  appearing  after 
the  yellowish-green  barium  flame  has  disappeared, 
indicates  calcium  or  strontium  or  both.  Through 
green  glass  the  calcium  flame  appears  green  and  the 
strontium  flame  faint  yellow  for  an  instant.  Through 
blue  glass  calcium  gives  a  faint  greenish-gray  and  stron- 
tium a  purple  or  rose  color. 

These  phenomena  exhibited  by  the  alkalies  and 
alkaline  earths  may  be  summarized  as  follows : 


Flame  Color. 

Through  Blue  Glass. 

Through  Green  Glass. 

Potassium 
Sodium 
Lithium 

Violet 
Yellow 
Carmine 

Reddish-violet 
Blue  to  invisible 
Violet-red 

Bluish-green 
Orange-yellow 
Invisible 

Barium 
Calcium 
Strontium 

Yellow-green 
Yellow-red 
Scarlet 

Green-gray 
Purple 

Bluish-green 
Green 
Faint  yellow 

The  detection  of  the  alkalies  in  silicates  is  accom- 
plished by  fusing  the  powdered  assay  on  platinum  wire 
with  a  little  pure  gypsum.  If  the  alkaline  earths  are 
sought  for,  the  assay  is  fused  with  sodium  carbonate 
on  platinum  wire,  or  better,  on  a  piece  of  platinum 
foil.  The  fused  mass  is  then  extracted  with  water  and 
the  residue  treated  with  hydrochloric  acid.  Silica 
will  be  precipitated,  leaving  in  the  solution  a  mixture 


146  MINERALS  AND  ROCKS 

of  sodium  chloride  and  the  chlorides  of  the  alkaline 
earths.  The  solution  is  then  tested  in  the  flame  with 
the  aid  of  a  clean  platinum  wire. 

The  Copper  Test. — An  almost  certain  test  for 
copper  and  for  chlorine  is  afforded  by  the  difference 
in  the  color  imparted  to  the  flame  by  copper  chloride 
and  most  other  copper  salts.  Several  substances 
besides  copper  give  green  flames,  but  in  the  case  of 
copper  alone  the  color  of  the  flame  is  changed  to  sky- 
blue  by  touching  the  assay  with  HC1,  or  a  chloride. 

Special  Tests. — A  few  tests  with  special  reagents 
are  so  characteristic  for  certain  elements  that  they  are 
specific : 

Tests  with  Na2CO3. — When  a  powdered  substance 
containing  S  is  fused  with  four  times  its  volume  of 
dry  Na2C03  and  heated  intensely  for  some  time  on 
charcoal,  the  residue,  when  placed  on  a  silver  coin  and 
moistened  with  water  or  hydrochloric  acid,  will  yield 
a  black  or  brown  stain.  This  reaction  is  due  to  the 
production  of  Na2S,  which  is  soluble.  The  solution 
containing  the  sulphide  reacts  with  the  silver,  pro- 
ducing insoluble  Ag2S,  which  is  brown  or  black. 
Thus:  Na2S+Ag2+H20+0  =  Ag2S+2NaOH.  Sul- 
phides and  sulphates  are  distinguished  by  roasting  the 
compound  on  charcoal  without  Na2C03.  Sulphides 
yield  the  sulphur-dioxide  odor. 

Manganese  and  chromium  compounds,  fused  with 
Na2COs  (especially  when  a  little  niter  is  added),  yield 
colored  masses — the  manganese  compound  a  bright 
green  mass  (Na2Mn04)  and  the  chromium  compounds 
a  bright  yellow  mass  (Na2Cr04).  In  the  case  of  the 
manganate,  the  reaction  may  be 

MnO2+Na2CO3+O  =  Na2MnO4+C02. 


DETERMINATION  OF  MINERALS  147 

Tests  with  the  Cobalt  Solution.  —  Certain  metallic 
oxides,  when  moistened  with  a  few  drops  of  a  solution 
of  crystallized  cobalt  nitrate  dissolved  in  ten  parts  of 
water,  and  heated,  yield  distinctive  colors  that  may 
often  serve  as  aids  in  their  detection.  The  assay 
is  powdered,  moistened  with  a  drop  of  the  cobalt  solu- 
tion, and  placed  on  charcoal  and  heated  intensely. 
Compounds  containing  alumina  yield  a  mass  of  a  blue 
color,  without  luster.  A  few  other  substances  may  also 
give  blue  masses,  but  the  materials  are  fused  and, 
consequently,  show  a  glassy  luster.  Magnesium  com- 
pounds give  a  pink  color. 

In  testing  for  other  substances,  it  is  necessary  first 
to  obtain  their  oxides.  This  is  done  by  roasting  on 
charcoal  until  a  distinct  sublimate  is  produced.  This 
sublimate  is  moistened  with  a  drop  of  the  solution  and 
heated  gently  by  the  O.F.  Under  these  conditions,  the 
white  zinc  sublimate  (ZnO)  changes  to  a  bright  yellow- 
ish-green and  tin  oxide  (Sn02)  to  a  bluish-green. 

Tests  with  Acid  Potassium  Sulphate.  —  Hydrogen 
potassium  sulphate  (HKSO4),  when  fused  with  a 
powdered  substance  in  a  closed  tube,  may  cause  the 
evolution  of  gases.  For  example: 


which  in  many  cases  may  easily  be  recognized. 

Nitrites  and  nitrates  yield  reddish-brown  fumes 
(NO2)  with  the  characteristic  odor  of  nitrogen  per- 
oxide. 

Chlorates  yield  a  yellowish-green  explosive  gas. 

Iodides  yield  a  violet  gas,  which  colors  blue  a  paper 
soaked  in  starch  paste,  when  a  little  Mn02  is  added 
to  the  HKSO4. 


148  MINERALS  AND  ROCKS 

Bromides  yield  a  reddish-brown  gas  (Br),  turning 
starch  paste  yellow,  when  Mn02  is  mixed  with  the 
HKS04. 

Chlorides  yield  hydrochloric  acid  (HC1),  recognized 
by  its  odor  and  the  voluminous  white  fumes  it  forms 
with  ammonia. 

Sulphides  yield  hydrogen  sulphide  (H2S)  with  its 
characteristic  odor.  This  gas  blackens  paper  moist- 
ened with  lead  acetate. 

Fluorides  yield  hydrofluoric  acid  (HF)  gas,  which 
has  a  pungent  odor  and  etches  glass.  The  etching  is 
due  to  the  reaction  between  the  Si02  of  the  glass  and 
theHF.  Thus,  Si02+4HF  =  SiF4+2H2O.  The  SiF4 
is  volatile  and  is  driven  up  the  tube,  leaving  tiny  pits 
from  which  the  SiO2  was  taken.  This  reaction  is  best 
seen  by  heating  the  assay  with  four  times  its  volume 
of  the  reagent  and  then  cleaning  and  drying  the  tube. 

The  reaction  is  more  delicate  if  the  finely  powdered 
assay  is  mixed  with  microcosmic  salt  and  heated  in  an 
open  tube.  When  the  salt  is  heated,  it  breaks  up,  yield- 
ing NaP03(HNa(NH4)P04-4H20  ='NaPO3  +  NH3 
+5H2O)  which  reacts  with  the  fluoride  as  follows: 

CaF2+NaPO3+H2O  =  CaNaP04+2HF. 

By  Reduction  with  Metallic  Zinc  and  Hydrochloric 
Acid  certain  metallic  salts  yield  colored  solutions  which 
are  characteristic.  The  substance  to  be  tested  is 
powdered  and  mixed  thoroughly  with  sodium  carbonate 
and  niter,  and  the  mass  is  slightly  moistened  and  placed 
in  a  little  spiral  at  the  end  of  a  fine  platinum  wire. 
After  fusion,  it  is  dissolved  in  a  little  water,  a  few  drops 
of  hydrochloric  acid  are  added  and  a  strip  of  zinc  or 
tin,  or  a  few  grains  of  the  metal,  are  then  placed  in 


DETERMINATION  OF  MINERALS  149 

the  solution.  The  hydrogen,  evolved  by  the  contact  of 
the  metal  and  the  acid,  reduces  the  oxides  and  the 
solution  becomes  colored.  The  most  important  oxides 
detectable  by  this  method  are: 

Molybdenum,  which  gives  a  blue,  then  green,  and 

finally  a  blackish-brown  solution. 
Tungsten,  a  blue,  then  brown  or  copper-red  solution. 
Vanadium,  a  blue  solution. 
Columbium,  a  blue  or  brown  solution  which  loses 

its  color  on  addition  of  water. 
Chromium,  a  green  solution. 
Titanium,  a  violet  solution. 
In  the  case  of  titanium  the  reactions  are: 

Ti02 +2Na2C03  =  Na4Ti04+2C02 ; 
Na4Ti04+8HCl  =  TiCl4+4NaCH-4H2O; 
TiCl4+H  =  TiCl3+HCl. 

The  TiCU  produces  the  violet  solution. 

Magnesium  ribbon  is  generally  employed  as  an  aid 
in  the  detection  of  phosphorus.  The  powdered  assay 
is  placed  in  the  bottom  of  a  closed  glass  tube  with  a 
piece  of  magnesium  ribbon  about  5  mm.  long,  so  that 
the  powder  is  in  close  contact  with  the  metal.  This 
is  then  heated  intensely  until  partial  fusion  ensues. 
The  completion  of  the  reaction  is  known  by  the  forma- 
tion of  a  brown  or  black  glass,  which  is  the  phosphide 
of  magnesium.  Upon  crushing  the  tube  and  moisten- 
ing its  contents  with  water  the  characteristic  odor  of 
of  phosphine  is  perceived  (the  odor  of  wet  phosphorus 
matches). 

Hydrochloric  acid  furnishes  the  readiest  test  for 
carbonates.  If  the  powdered  substance  is  heated 
gently  with  dilute  acid  in  a  test  tube,  a  brisk  efferves- 


150  MINEEALS  AND  ROCKS 

cence  will  result  if  it  contains  the  carbonic  acid  radical. 
Sometimes  the  effervescence  can  be  detected  by  hold- 
ing the  mouth  of  the  test  tube  to  the  ear,  even  when  the 
escape  of  gas  cannot  be  seen.  The  gas  (062)  is  color- 
less, and  when  allowed  to  bubble  through  lime  water 
will  cause  turbidity. 


IV 


CHARACTERISTIC    REACTIONS    OF    THE    MORE 
IMPORTANT  ELEMENTS  AND  ACID  RADICALS 

Aluminium  (p.  147). — Fusible  minerals  cannot  be 
satisfactorily  tested  •  for  Al  by  the  method  using 
Co(NOs)2,  since  cobalt  imparts  a  blue  color  to  all 
glasses. 

Since  zinc  silicates  yield  the  same  color  reaction 
with  Co(NOa)2  as  do  infusible  aluminium  compounds, 
the  presence  of  aluminium  in  silicates  cannot  be 
assured  unless  the  absence  of  zinc  is  proven. 

Antimony  (pp.  135, 136, 138,  143).— In  the  presence 
of  lead  or  bismuth,  the  assay  is  heated  on  charcoal  with 
fused  boric  acid,  which  dissolves  the  lead  and  bismuth 
oxides,  while  the  antimony  oxide  coats  the  charcoal. 

When  antimony  and  lead  are  present  in  the  same 
compound,  the  antimony  oxide  forms  a  white  incrus- 
tation surrounding  a  dark  orange-yellow  incrustation 
of  lead  antimonate. 

Arsenic  (pp.  135,  136,  138,  143). — Arsenic  in  arse- 
nates  and  arsenites  may  usually  be  detected  by  heating 
the  powdered  assay  with  six  times  its  volume  of  a  mix- 
ture of  equal  parts  of  Na2COs  and  KCN  (or  pow- 
dered charcoal)  in  a  dry  closed  glass  tube,  when  an 
arsenic  mirror  will  form  on  the  cold  part  of  the  tube. 
This  may  be  further  tested  by  breaking  off  the  end 
of  the  tube  and  heating  the  mirror  in  the  burner 

151 


152  MINERALS  AND  ROCKS 

flame.  The  escaping  fumes  will  have  the  charac- 
teristic garlic  odor.  If  allowed  to  pass  through  the 
flame,  they  will  tinge  it  violet. 

If  there  is  doubt  as  to  whether  a  white  sublimate 
on  charcoal  contains  arsenic,  or  if  it  is  desired  to  test 
for  arsenic  in  the  presence  of  antimony,  a  little  of  the 
coating  which  is  farthest  away  from  the  assay  may 
be  scraped  from  the  surface  of  the  charcoal  and 
placed  in  a  narrow  glass  tube  and  heated.  If  arsenic 
oxide  is  present  in  the  coating,  the  arsenic  mirror 
will  form  on  the  walls  of  the  cooler  part  of  the  tube. 

Barium  (pp.  143,  145). — Before  applying  the  flame 
test  for  barium,  silicates  should  first  be  fused  with  four 
parts  of  dry  Na2COs  and  charcoal  in  a  loop  of  plati- 
num wire,  crushed,  placed  in  a  test  tube,  treated  with 
a  few  cc.  of  dilute  HNOs  and  evaporated  to  dryness. 
After  cooling,  warm  with  a  very  little  HC1,  then  add 
about  10  cc.  of  water  and  filter  off  the  insoluble  silica. 
To  the  filtrate  add  a  few  drops  of  H2S04,  collect  the 
precipitate  on  a  small  filter,  and  test  with  the  flame 
(see  also  under  Calcium). 

Bismuth  (pp.  135,  139). — A  very  characteristic  test 
is  the  following:  The  powdered  substance  is  mixed 
with  twice  its  volume  of  a  mixture  composed  of  equal 
parts  of  KI  and  flowers  of  sulphur,  and  heated  in  the 
R.F.  on  charcoal.  If  Bi  is  present,  a  brick-red  iodide 
of  bismuth  will  form  a  coating  at  some  little  distance 
from  the  assay.  This  test  serves  to  distinguish  be- 
tween Pb  and  Bi,  both  of  which  yield  yellow  oxide 
coatings  when  tested  on  charcoal. 

Boron  (p.  143). — To  obtain  the  green  flame  in 
the  case  of  most  compounds  containing  boron,  it  is 
sufficient  to  moisten  the  fine  powder  with  a  drop  of 


CHARACTERISTIC  REACTIONS  153 

strong  sulphuric  acid  and  introduce  a  small  quantity 
into  the  flame  on  a  platinum  wire.  The  flame  will 
be  colored  green,  but  only  for  a  moment.  More 
resistant  compounds,  like  the  silicates,  must  be  fused 
with  a  flux  composed  of  one  part  of  powdered  fluorspar 
and  four  parts  of  KHSO4  before  the  green  coloration 
can  be  obtained.  The  HF  generated  decomposes  the 
silicate  and  sets  free  the  boron. 

In  the  presence  of  copper  compounds  or  phosphates, 
which  also  give  green  flames,  the  finely-powdered 
assay  is  moistened  on  platinum  foil  with  sulphuric 
acid.  The  excess  of  acid  is  then  removed  by  heating, 
and  the  powder  mixed  into  a  paste  with  glycerine 
and  a  little  sodium  carbonate.  When  heated  in  the 
flame,  the  sodium  will  mask  the  green  color  due  to 
the  copper  and  phosphorus,  but  not  that  produced 
by  boron. 

If  boron  compounds  are  fused  with  Na2COs  and 
then  treated  with  dilute  HC1,  a  drop  of  the  resulting 
solution  will  cause  turmeric  paper  to  turn  reddish- 
brown  after  being  dried  at  100°.  If  moistened  with 
ammonia,  the  color  changes  to  black. 

Bromine  (p.  148). — Solutions  of  bromides,  produced 
by  dissolving  in  water  or  HNOs  (after  fusion  with 
Na2COs  if  insoluble  otherwise),  will  yield  with  a  drop 
or  two  of  silver  nitrate  solution  a  yellowish  precipi- 
tate of  AgBr,  which  is  soluble  in  ammonia.  If  this 
precipitate  is  mixed  with  Bi2Ss  and  heated  in  a  closed 
tube,  a  yellowish  sublimate  of  BiBr3  will  result. 
(Compare  Chlorine  and  Iodine.) 

Cadmium  (p.  139). — When  present  with  Pb  or  Zn, 
it  is  often  difficult  to  recognize  the  cadmium  coating 
on  charcoal.  In  this  case,  the  coating  may  be  scraped 


154  MINERALS  AND  ROCKS 

from  the  coal  and  heated  very  gently  in  the  closed 
tube.  A  yellow  sublimate  of  cadmium  oxide  will 
form  just  above  the  assay.  On  further  heating,  this 
will  be  masked  by  the  zinc  and  lead  oxides. 

Calcium  (pp.  143,  145). — Calcium  in  silicates  and 
other  insoluble  compounds  may  be  detected  by  the 
same  method  as  that  for  the  detection  of  barium. 
The  precipitate  of  CaS04,  however,  is  dissolved  when 
heated  with  a  large  volume  of  water. 

Carbonates. — See  page  149. 

Chlorine  (pp.  146,  147,  148).— Chloride  solutions, 
when  treated  with  AgNOs,  yield  a  white  precipitate 
of  AgCl,  soluble  in  ammonia.  When  exposed  to  the 
light,  it  darkens.  If  mixed  with  Bi2Ss  and  heated  in 
a  closed  tube,  a  white  sublimate  of  Bi2Cl3  is  formed. 
(Compare  Bromine  and  Iodine.) 

Chromium  (pp.  141,  146,  149). — In  the  presence  of 
large  quantities  of  iron,  copper,  etc.,  the  powdered 
assay  (if  not  a  silicate)  is  mixed  with  double  its 
volume  of  equal  parts  of  Na2COs  and  K2N03  and 
fused  on  a  platinum  spiral  in  the  O.F.,  when  an 
alkaline  chromate  will  be  formed.  This,  dissolved  in 
water  and  boiled  with  an  excess  of  acetic  acid,  yields 
a  solution  which  gives  a  yellow  precipitate  of  PbCr04 
with  a  few  drops  of  lead  acetate. 

Silicates  containing  small  quantities  of  chromium 
and  large  quantities  of  copper  and  iron  should  first 
be  fused  on  charcoal  with  a  mixture  of  one  part  of 
sodium  carbonate  and  a  half  part  of  borax.  The 
clear  glass  thus  produced  is  dissolved  in  hydrochloric 
acid  and  the  solution  evaporated  to  dryness.  This  is 
then  treated  with  water,  filtered,  and  the  filtrate 
boiled  with  a  few  drops  of  nitric  acid  to  oxidize  the 


CHARACTERISTIC  REACTIONS  155 

iron.  By  the  addition  of  ammonia,  the  chromic  and 
other  oxides  are  precipitated.  The  precipitate  is 
collected  on  a  filter,  washed,  and  treated  as  above, 
or  tested  with  the  borax  bead. 

Cobalt  (p.  141). — For  the  detection  of  cobalt  in  the 
presence  of  iron  or  nickel,  see  under  those  metals. 

Columbium  (pp.  141,  149). — When  a  compound 
containing  columbium  is  fused  with  five  parts  of  borax 
on  platinum  foil,  dissolved  in  concentrated  HC1  and 
diluted  with  a  little  water,  the  solution  becomes  blue 
when  boiled  with  the  addition  of  granulated  tin.  The 
color  does  not  change  to  brown  on  continued  boiling. 
It  disappears,  however,  when  diluted  with  water.  If 
titantium  is  present  in  the  same  solution,  its  color 
will  be  first  violet,  then  blue.  Tungsten,  which  gives 
a  blue  solution  under  the  same  conditions,  can  be  dis- 
tinguished from  columbium  by  the  bead  test.  If, 
instead  of  tin,  the  solution  is  boiled  with  zinc,  its 
color  changes  rapidly  from  blue  to  brown. 

Or,  the  finely-powdered  substance  may  be  fused  in 
a  test  tube  or  crucible  with  ten  parts  KHSO4,  and  then 
digested  with  cold  water  for  a  long  time.  If  columbium 
is  present,  an  insoluble  white  residue  will  be  left. 
This,  if  collected  on  a  filter,  washed,  and  then  treated 
in  a  test  tube  with  hot  concentrated  HC1,  will  yield 
the  blue  solution  when  boiled  with  granulated  tin. 

Copper  (pp.  141,  143,  146). — A  very  delicate  test 
for  soluble  copper  compounds  is  to  dissolve  them  in 
HC1  or  HNOs,  dilute  with  water  and  add  ammonia  in 
excess.  A  deep  purple-blue  solution  of  CuCl2-6NH3 
or  Cu(NO3)2-6NH3  will  result. 

Fluorine  (pp.  135,  148). — If  the  mineral  to  be  tested 
is  a  silicate,  its  powder  is  mixed  with  four  parts  of 


156  MINERALS  AND  ROCKS 

fused  microcosmic  salt  and  this  mixture  is  heated  in  a 
closed  tube.  If  fluorine  is  present,  the  glass  above  the 
assay  will  be  etched  by  the  HF  produced.  At  the 
same  time,  a  ring  of  Si02  is  deposited  in  the  cool  por- 
tion of  the  tube  in  consequence  of  the  reaction 

3SiF4+2H2O  =  2H2SiF6+SiO2. 

Upon  heating,  the  ring  moves  up  the  tube  to  a  cooler 
portion. 

Gold  (p.  138). — The  metal  is  best  detected  by  treat- 
ment with  aqua-regia  of  the  metallic  bead,  produced  by 
fusion  with  Na2CO3  on  charcoal.  This  yields  a  light- 
yellow  solution,  which,  when  taken  up  on  a  filter 
paper  and  moistened  with  stannous  chloride,  gives  the 
"  purple  of  Cassius." 

Or,  if  the  mineral  is  to  be  tested  for  free  gold,  it 
is  powdered  and  treated  with  aqua-regia  and  the  solu- 
tion diluted  and  filtered.  The  filtrate  is  evaporated 
nearly  to  dryness,  diluted  with  water  and  a  few  drops 
of  a  solution  of  ferrous  sulphate  are  added.  If  gold 
is  present  in  small  quantity  only,  the  solution  will  be 
colored  bluish  or  purple.  If  the  gold  is  present  in 
larger  quantity,  the  metal  will  be  precipitated  as  a 
brown  powder. 

Free  gold  may  also  be  detected  by  powdering  the 
substance  until  all  will  pass  through  a  fine  sieve. 
Brush  the  material  adhering  to  the  sieve  and  add  to 
the  powder.  Then  place  in  a  basin  containing  a  little 
mercury  (f  cc.)  and  immerse  the  basin  and  its  contents 
in  water.  Shake  the  basin  gently  with  a  rocking 
motion  and  gradually  allow  the  rock  powder  to  escape. 
The  gold  will  fall  to  the  bottom  and  amalgamate  with 
the  mercury.  After  the  mass  has  been  reduced  to  a 


CHAKAGTERISTIC  EEACTIONS  157 

small  volume,  transfer  to  a  mortar  and  grind  in  a 
gentle  stream  of  water,  until  nothing  but  the  amalgam 
is  left.  Then  place  in  an  iron  spoon  and  heat  in  the 
open  air  until  all  the  mercury  is  driven  off;  or  the 
amalgam  may  be  placed  in  a  shallow  cavity  on  char- 
coal and  heated  with  a  small  blowpipe  flame  until 
all  the  mercury  volatilizes.  The  residual  gold  may  be 
collected  into  a  globule  by  placing  a  little  borax  or 
sodium  carbonate  in  the  cavity  and  heating  until  quiet 
fusion  takes  place. 

When  driving  off  the  mercury  from  the  amalgam 
extreme  care  must  be  taken  not  to  breathe  its  fumes  since 
they  are  poisonous.  The  operation  should  not  be  per- 
formed in  a  closed  room. 

Iodine  (p.  147). — Substances  containing  iodine, 
when  fused  in  a  glass  tube  with  KHS04  and  MnCb, 
yield  a  vapor  which  is  recognized  as  that  of  iodine  by 
its  violet  color.  In  the  presence  of  other  halogens, 
iodine  may  be  detected  by  mixing  the  powdered  sub- 
stance with  BiSs  (prepared  by  fusing  together  small 
quantities  of  bismuth  and  sulphur)  and  heating  in  a 
closed  tube  or  on  charcoal  before  the  blowpipe.  If 
iodine  is  present,  a  red  sublimate  of  bismuth  iodide 
is  produced.  (Compare  Chlorine  and  Bromine.) 

Iron  (pp.  135,  138,  141). — To  distinguish  ferrous 
and  ferric  conditions,  the  assay  is  added  to  a  borax 
bead  containing  copper.  If  the  iron  is  in  the  ferric  con- 
dition, the  bead  will  be  bluish-green;  if  in  the  ferrous 
condition,  it  will  contain  red  streaks  of  cuprous  oxide. 

In  the  presence  of  easily  fusible  metals  like  lead, 
tin,  zinc,  etc.,  the  substance  is  heated  on  charcoal 
with  borax  in  the  R.F.  The  easily  reducible  metals 
do  not  become  oxidized  and,  consequently,  are  not 


158  MINERALS  AND  ROCKS 

absorbed  by  the  glass.  The  glass  is  separated  from  the 
metallic  bead,  and  is  heated  on  a  fresh  piece  of  charcoal 
in  the  R.F.,  when  it  acquires  the  characteristic  bottle- 
green  color  produced  by  iron,  and  becomes  vitriol-green 
on  addition  of  tin. 

In  the  presence  of  cobalt,  the  blue  color  of  the 
cobalt  bead  masks  the  green  of  the  iron  bead.  In 
this  case,  iron  is  detected  by  heating  the  blue  glass 
on  platinum  wire  in  the  O.F.  sufficiently  long  to 
convert  all  the  iron  into  peroxide.  With  very  little 
iron  present,  the  bead  is  green  when  hot,  and  blue 
when  cold;  with  more  iron  the  bead  is  dark  green 
when  hot,  and  pure  green  when  cold,  this  latter  color 
resulting  from  a  mixture  of  the  yellow  iron  and  the 
blue  cobalt  colors. 

Manganese  colors  the  borax  bead  in  the  O.F.  red. 
Upon  reduction  with  tin  on  charcoal,  the  bead  becomes 
bottle-green.  If  cobalt  also  is  present,  the  bead  pro- 
duced in  the  O.F.  is  dark  violet.  In  the  R.F.  it  be- 
comes green  when  hot  and  blue  when  cold. 

Lead  (pp.  135,  139,  143).— The  coating  of  lead 
oxide  resembles  very  closely  that  of  bismuth.  The  two 
may  be  distinguished  by  the  proceeding  described 
under  bismuth.  The  iodide  of  lead  is  lemon-yellow. 

Lithium  (pp.  143,  144,  145). — In  the  case  of  sili- 
cates, before  testing  for  flame  coloration,  it  is  advisable 
to  mix  the  powder  of  the  assay  with  one  part  of  fluor- 
spar and  one  and  a  half  parts  of  KHSO4  and  form  into 
a  paste  with  a  drop  of  water.  If  boron  is  present,  the 
flame  is  at  first  green,  then  red.  The  presence  of  phos- 
phoric acid  is  shown  by  the  production  of  a  green  flame 
together  with  the  red  one.  This  is  especially  notice- 
able after  moistening  the  assay  with  sulphuric  acid. 


CHARACTERISTIC  REACTIONS  159 

Magnesium  (p.  147).— The  Co(NO3)2  test  for  mag- 
nesium is  applicable  only  to  white  or  colorless  minerals 
and  is  by  no  means  conclusive.  The  most  satisfactory 
test  is  that  employed  generally  in  ordinary  qualitative 
analysis,  viz.,  precipitation  with  the  aid  of  sodium 
phosphate  (NasPCU).  The  powdered  mineral,  if 
insoluble  in  acids,  is  fused  with  Na2COs,  powdered, 
dissolved  in  a  few  cc.  of  dilute  HNOs  and  evaporated  to 
dryness.  It  is  then  dissolved  in  2  or  3  cc.  HC1  and 
warmed  for  a  few  minutes.  There  is  next  added  about 
10  cc.  of  water  and  the  solution  is  boiled  and  filtered 
to  remove  silica.  The  filtrate  is  heated  to  boiling  and 
NH4OH  is  added  to  slight  excess  to  precipitate  iron 
and  aluminium.  This  is  now  filtered  and  the  filtrate 
is  boiled  again,  and  to  it  is  added  some  ammonium 
oxalate  to  separate  calcium.  After  allowing  it  to 
stand  for  ten  or  fifteen  minutes,  the  calcium  oxalate  is 
removed  by  several  filtrations  until  the  filtrate  is  clear. 
To  the  filtrate  a  solution  of  sodium  phosphate  and 
strong  ammonia  are  added.  If  magnesium  is  present 
after  standing  for  some  time,  a  fine  white  crystalline 
precipitate  of  NH4MgP04-6H2O  will  form. 

Manganese  (pp.  141, 146). — Manganese  compounds 
soluble  in  HNOs  are  readily  detected  by  oxidation 
with  persulphates.  The  procedure  is  to  dissolve  in 
a  few  cc.  of  moderately  dilute  HNOs  (sp.gr.  1.2), 
add  about  one-half  its  volume  of  dilute  solution  of 
AgNOs  and  a  few  drops  of  ammonium  persulphate 
(200  gr.  (NH4)2S20s  to  one  liter  of  water)  and  gently 
heat.  The  manganese  will  be  oxidized  to  permanganic 
acid,  which  is  purple.  The  reaction  is 

2Mn(NO3)2+5(NH4)2S208+8H2O 
=  5(NH4)2SO4+5H2SO4+4HNO3+2HMnO4. 


160  MINERALS  AND  ROCKS 

Compounds  that  are  insoluble  in  HNO3  must  first  be 
fused  with  Na2C(>3  on  charcoal. 

Mercury  (p.  135). — In  the  presence  of  sulphur,  chlo- 
rine, iodine  and  a  few  acids,  the  assay  is  best  heated 
with  dry  Na2COs  in  a  closed  glass  tube.  The  acid 
combines  with  the  sodium  and  the  mercury  sublimes. 

Molybdenum  (pp.  138,  139,  141,  143,  149).— The 
white  coating  of  MoOs  on  charcoal,  if  touched  with  the 
R.F.,  is  partly  reduced,  becoming  blue.  If  heated  by 
the  O.F.,  some  of  it  volatilizes,  but  some  is  reduced  by 
the  charcoal,  forming  a  copper-red  coating. 

Small  quantities  of  molybdenum  are  detected  by 
treating  the  powdered  assay  with  a  little  strong  sul- 
phuric acid  on  a  platinum  foil.  After  heating  until 
most  of  the  acid  is  evaporated,  and  then  cooling,  the 
resulting  mass  becomes  blue,  particularly  after  being 
repeatedly  breathed  upon,  or  after  being  moistened 
with  alcohol  and  dried  by  heating. 

Nickel  (pp.  138,  141). — In  the  presence  of  Co,  the 
color  of  the  Ni  borax  bead  is  often  masked.  In  such 
cases,  a  small  portion  of  the  mineral  is  fused  in  the 
R.F.  to  a  globule.  A  fragment  of  borax  "  twice  the  size 
of  the  globule  is  placed  beside  it  on  charcoal  and  the 
two  are  heated  by  the  O.F.  The  two  globules  will  roll 
around  under  the  flame  in  contact,  but  will  remain 
quite  distinct;  any  cobalt  will  be  oxidized  by  the  O.F. 
and  be  absorbed  by  the  borax,  which  will  become  blue. 
If  the  mineral  is  placed  upon  a  clean  part  of  the  coal 
and  the  treatment  is  continued  with  fresh  portions 
of  borax  until  all  the  cobalt  has  been  oxidized  and 
the  borax  no  longer  becomes  blue,  the  nickel  present 
will  impart  its  characteristic  violet  and  reddish-brown 
color  to  the  borax."  (Phillips.) 


CHARACTERISTIC  REACTIONS  161 

Nickel  is  best  detected  by  treating  its  solution  with 
dimethyl  glyoxime  ((CH3)2C2(NOH)2).  The  assay  is 
dissolved  in  acid,  after  fusion  with  Na2CO3,  if  necessary, 
and  the  solution  is  neutralized  with  (NH^OH.  Add 
one-half  volume  of  dimethyl  glyoxime  solution,  made 
by  dissolving  one  part  of  the  compound  in  100  pts.  of 
a  40  per  cent,  alcohol,  and  again  add  a  little  (NH^OH 
to  neutralize.  A  bright  red  crystalline  precipitate 
will  form  if  nickel  is  present,  according  to  the  reaction : 

NiCl2+2(CH3)2C2(NOH)2 
=  (CH3)  2C2  (NOH)  2  -  (CH3)  2C2  (NO)  2Ni+2HCl. 

Nitric  Acid  (pp.  135,  143,  147). — Nitric  acid  is  best 
detected  by  dissolving  the  assay  in  dilute  (1 : 1)  H2SO4, 
cooling  and  adding  to  the  solution  in  a  test  tube  a 
few  drops  of  a  strong  solution  of  FeSCU  in  water, 
holding  the  tube  slanting  and  allowing  the  FeSCU  to 
trickle  quietly  down  its  side  and  form  a  layer  upon  the 
acid  solution.  If  nitrates  are  present,  a  brown  ring 
will  form  at  the  contact  of  the  two  solutions. 

Oxygen,  in  some  of  the  higher  oxides,  may  be  de- 
tected by  the  liberation  of  chlorine  when  they  are 
treated  with  HC1.  This  is  particularly  the  case  with 
the  higher  oxides  of  manganese,  thus : 

MnO2+4HCl  =  MnCl2+2H2O+2Cl. 

The  chlorine  is  recognized  by  its  color,  its  odor  and  its 
bleaching  action. 

Phosphoric  Acid  (pp.  143,  149). — In  the  test  with 
magnesium  ribbon,  it  is  best  to  fuse  the  phosphates  of 
Al  and  the  heavy  metals  with  two  parts  of  Na2C03  on 
charcoal,  to  remove  and  grind  up  the  fused  mass,  and 


162  MINERALS  AND  ROCKS 

then  to  ignite  the  powder  with  magnesium  ribbon 
in  a  closed  glass  tube  (Brush  and  Penfield). 

If  a  small  crystal  of  ammonium  molybdate 
(NH^MoCU  be  placed  on  a  phosphate  and  a  little 
dilute  HNOs  be  dropped  upon  it,  the  crystal  will  turn 
yellow  in  consequence  of  the  production  of  ammonium 
phosphomolybdate  ll(MoO3)  •  (NH4)3P04.  This  test  is 
available  only  for  compounds  that  are  soluble  in.  HNO3. 

If  the  mineral  is  insoluble  in  HNOs,  it  must  first 
be  fused  with  sodium  carbonate  on  platinum  wire. 
The  bead  is  then  dissolved  in  nitric  acid  and  the  solu- 
tion when  cold  is  added  drop  by  drop  to  a  little  of  an 
ammonium  molybdate  solution  and  allowed  to  stand 
without  warming.  If  the  assay  contained  the,  phos- 
phoric acid  radical,  a  yellow  precipitate  will  be  formed. 

Potassium. — See  pages  144  and  145. 

Selenium  (pp.  136,  139,  143).— Selenates  and  sele- 
nites  must  be  reduced  with  sodium  carbonate  on  char- 
coal before  the  peculiar  odor  is  evolved. 

Silicon  (p.  141). — Small  splinters  of  silicates  yield 
an  infusible  skeleton  of  silica  when  heated  in  a  bead 
of  microcosmic  salt.  This  floats  around  in  the  liquid 
bead  as  a  particle  with  the  shape  of  the  original  splinter 
or  as  a  transparent  flake.  In  some  cases  tho  original 
splinter  remains  undecomposed. 

Many  silicates  decompose  in  strong  HNO4  or  HC1 
with  the  production  of  a  gelatinous  mass  of  silicic  acid. 
If  the  solution  containing  the  gelatinous  silica  is 
evaporated  to  dryness,  the  silica  becomes  insoluble 
and  remains  as  a  residue  when  the  mass  is  warmed  with 
a  little  strong  acid  and  digested  with  water. 

In  case  of  insoluble  silicates  it  is  necessary  to  fuse 
with  Na2COs  before  proceeding  with  the  test.  The 


CHARACTERISTIC  REACTIONS  163 

fusion  results  in  the  production  of  a  sodium  silicate 
which  is  soluble  in  acids.  The  gelatinous  precipitate 
will  appear  only  after  the  acid  solution  of  the  fused 
mass  is  evaporated. 

Silver. — See  page  138. 

Sodium. — See  pages  143,  144  and  148. 

Strontium  (pp.  143,  145). — In  the  case  of  insoluble 
compounds  treat  as  in  the  test  for  Ba.  If  both  Ba  and 
Sr  are  present  in  the  final  precipitate,  the  flame  will 
first  be  crimson.  Upon  repeated  moistening  with  HC1 
and  heating,  the  Sr  will  gradually  disappear  and  the 
green  color  of  the  Ba  flame  will  be  seen. 

Sulphur  (pp.  134,  136,  146,  148).— If  a  substance 
containing  sulphur  is  heated  with  Na2COs  on  charcoal 
in  the  R.F.  and  the  fused  mass  is  transferred  to  a 
watch  glass  and  moistened  with  water,  the  addition  of 
a  little  dilute  solution  of  ammonium  molybdate,  to 
which  HC1  has  been  added,  will  produce  a  blue  color. 

Sulphides  are  distinguished  from  most  sulphates 
(except  those  containing  water  or  the  OH  group)  by 
heating  in  the  O.F.  The  sulphides  yield  an  odor  of 
S(>2.  The  sulphates  yield  no  odor.  Another  means 
of  distinguishing  between  these  two  classes  of  com- 
pounds is  as  follows:  The  finely-powdered  substance  is 
fused  with  caustic  potash  (KOH),  in  a  platinum  spoon, 
or  on  a  piece  of  platinum  foil.  The  spoon  or  foil  with 
its  contents  is  thrown  into  water  containing  a  strip 
of  silver.  If  the  silver  remains  quite  white,  the  S  is 
present  as  sulphate;  if  the  silver  becomes  black,  S  is 
present  as  sulphide.  Substances  exercising  a  reducing 
action  must,  of  course,  not  be  present. 

Tantalum  cannot  be  recognized  in  the  presence  of 
columbium  by  any  simple  tests. 


164  MINERALS  AND  ROCKS 

Tellurium  (pp.  135;  136;  139).— A  powdered  tel- 
lurium compound,  heated  with  Na2C03  and  charcoal 
powder  in  a  closed  glass  tube  and  treated  when  cold 
with  hot  water,  yields  a  purple-red  solution  of  sodium 
telluride.  This  color  will  disappear  if  air  is  blown 
through  the  solution. 

Tellurides  may  be  detected  by  gently  warming  the 
finely-powdered  substances  with  a  few  cc.  of  con- 
centrated sulphuric  acid.  The  solution  will  become 
carmine.  After  cooling,  the  addition  of  water  will 
precipitate  the  tellurium  as  a  blackish-gray  powder, 
and  the  carmine  color  will  disappear. 

Thallium.— See  page  143. 

Tin  (pp.  139, 147). — The  reduction  of  tin  compounds 
is  accomplished  fairly  easily  by  mixing  borax  with 
Na2C03  and  treating  with  the  R.F.  on  charcoal. 
The  metallic  tin  thus  obtained,  when  heated  on  char- 
coal by  the  O.F.,  yields  a  white  incrustation  which 
becomes  bluish-green  when  moistened  with  cobalt 
nitrate  and  heated  (see  Zinc).  Or,  if  warmed  in  a 
test  tube  with  moderately  dilute  HNOs,  a  white 
powdery  metastannic  acid  (H^SnOs)  will  result. 

If  to  a  borax  bead  colored  blue  by  a  copper,  a  small 
quantity  of  tin  compound  be  added  and  the  R.F. 
be  applied,  the  bead  will  turn  brown. 

Titanium  (pp.  141, 149). — If  iron  is  present,  the  bead 
of  microcosmic  salt  in  the  O.F.  has  the  iron  color,  and 
in  the  R.F.  a  blood-red  color.  When  this  is  fused  with 
tin  in  the  R.F.  on  charcoal,  the  color  becomes  violet. 

A  very  characteristic  reaction  is  obtained  as  fol- 
lows: Fuse  on  charcoal  or  platinum  foil  one  part  of 
the  assay  with  6  parts  of  Na2C03  and  a  little  borax. 
Then  dissolve  in  a  small  quantity  of  concentrated 


CHAEACTERISTIC  REACTIONS  165 

HC1  (2-2.5  cc.)  and  add  granulated  tin.  The  hydro- 
gen generated  by  the  tin  and  HC1  will  reduce  the 
TiCU  in  the  original  acid  solution  to  TiCl3  and  the 
solution  will  assume  a  violet  color,  especially  after 
standing  several  hours. 

For  an  extremely  delicate  test,  fuse  the  powdered 
assay  with  Na2C03  and  borax,  as  in  the  color  test 
with  tin.  If  the  fused  mass  is  dissolved  by  heating 
in  a  test  tube  with  2  cc.  of  a  mixture  of  equal  parts 
of  H2S04  and  water,  and,  after  cooling,  is  diluted  with 
about  10  cc.  of  cold  water,  the  addition  of  a  few 
drops  of  H202  to  the  diluted  solution  will  produce  a 
golden  yellow  or  orange  color  if  titanium  is  present. 

Tungsten  (pp.  138,  141,  149).— When  present  in 
small  quantities,  tungsten  may  be  detected  by  fusing 
the  assay  with  five  or  six  times  its  weight  of  Na2COs, 
extracting  the  resulting  mass  with  water,  filtering 
and  adding  to  the  filtrate  strong  hydrochloric  acid. 
White  tungstic  oxide  (WO 3)  will  be  precipitated  and 
this  will  become  pale  yellow  on  boiling.  Upon  acidi- 
fication and  boiling  with  a  few  particles  of  tin,  a  blue 
mixture  of  oxides  results.  The  blue  color  will  not 
disappear  on  the  addition  of  water.  (Compare  tests 
for  Columbium.}  On  long-continued  boiling,  the  color 
will  change  to  brown  (W02). 

If  the  tungstate  be  decomposed  by  boiling  with 
HC1,  it  is  not  necessary  to  fuse.  Simply  boil  with 
acid  until  a  light  yellow  precipitate  (WO 3)  is  ob- 
tained. Then  add  tin  and  boil,  and  the  blue  color 
will  result.  This  will  change  to  brown  on  long-con- 
tinued boiling  (W02). 

Uranium  (p.  141). — If  the  uranium  is  so  mixed  with 
other  metals  that  its  characteristic  bead  is  obscured, 


166  MINERALS  AND  ROCKS 

dissolve  the  assay  in  HC1  (first  fusing  with 
or  borax,  if  necessary),  then  nearly  neutralize  with 
ammonia  "and  add  a  strong  solution  of  Na2COs  until 
precipitation  ceases,  then  about  half  as  much  more 
and  let  stand  for  some  time.  The  excess  of  Na2COs 
will  dissolve  the  compound  first  precipitated.  Filter, 
acidify  the  filtrate  with  HC1  and  boil  until  all  the 
C02  is  expelled.  Then  add  ammonia  in  excess.  If 
uranium  is  present,  it  will  be  precipitated  as  a  gelat- 
inous light  yellow  ammonium  uranate,  (NELi)  211267. 
To  confirm,  filter  and  test  the  precipitate  in  the  bead 
of  microcosmic  salt. 

Vanadium  (pp.  141,  149). — Vanadium  compounds, 
first  roasted  on  charcoal  and  then  fused  with  four  parts 
Na2COa  and  two  parts  potassium  nitrate  on  a  platinum 
spiral,  when  extracted  with  hot  water,  filtered,  acidi- 
fied with  acetic  acid,  and  treated  with  a  few  drops 
of  lead  acetate,  yield  a  pale  yellow  precipitate  of 
Pba(VO4)2.  This  may  be  tested  for  vanadium  in 
a  microcosmic  salt  bead. 

If  the  solution  obtained  by  extracting  the  fused 
mass  be  filtered  and  acidified  with  HC1  and  well 
shaken  with  hydrogen  peroxide,  it  will  become  reddish- 
brown  or  garnet  color.  If  to  the  acidified  solution 
metallic  zinc  be  added,  a  bright  blue  color  will  result. 
This,  however,  will  gradually  become  violet  if  the 
solution  is  left  standing  in  contact  with  zinc. 

If  the  substance  is  soluble  in  HC1  or  H2S04,  the 
solution  thus  produced  will  give  a  reddish-brown 
solution  with  hydrogen  peroxide,  or  a  blue  solution 
when  treated  with  zinc.  The  blue  solution  gradually 
changes  to  violet  on  continued  action  of  the  zinc.  If 
the  blue  or  violet  solution  is  poured  off  the  zinc  and 


CHARACTERISTIC  REACTIONS  167 

a  few  drops  of  hydrogen  peroxide  be  added,  the  char- 
acteristic brown  color  will  result.  For  a  more  accu- 
rate determination  of  the  presence  of  vanadium,  add 
NH4OH  in  excess  to  the  acid  solution  and  pass  through 
it  EbS.  The  solution  will  become  garnet  if  vanadium 
is  present. 

Zinc  (pp.  135,  139,  147).— Infusible  white  or  light- 
colored  zinc  compounds,  when  finely  powdered  and 
made  into  a  paste  with  a  drop  of  Co(N03)2  solution, 
and  then  heated  on  charcoal  by  an  O.F.,  assume  a 
green  color.  But  silicates  of  zinc  when  treated  in  this 
way  with  a  hot  flame  often  form  a  fusible  cobalt  sili- 
cate which  is  blue. 

In  the  presence  of  antimony  and  tin,  it  is  almost 
impossible  to  detect  zinc  by  blowpipe  tests,  as  all  three 
metals  yield  nearly  the  same  blowpipe  reactions. 
However,  the  zinc  sublimate  when  moistened  with 
Co(NOs)2  solution  and  heated  in  the  O.F.  becomes 
grass-green,  whereas  the  tin  sublimate,  under  the 
same  treatment,  becomes  blue-green. 

Zirconium,  in  the  absence  of  titanium,  molybdates 
and  boric  acid,  may  be  detected,  after  fusion  of  the 
assay  with  a  little  Na2COs,  by  dissolving  in  a  few  drops 
of  strong  HC1  and  diluting  with  water  to  four  times 
the  volume,  and  then  moistening  with  this  dilute 
solution  a  piece  of  turmeric  paper.  When  the  paper 
is  dried  gently  its  color  will  change  to  reddish  or  orange 
if  zirconium  is  present. 


KEY   TO   THE    DETERMINATION    OF   MINERALS 

A  "  KEY"  in  mineralogy  is  a  guide  to  aid  in  the  deter- 
mination of  the  name  and  nature  of  a  mineral.  The 
most  serious  objection  to  its  use  lies  in  the  danger 
that  the  student  will  feel,  when  the  name  of  the  sub- 
stance under  examination  is  obtained,  that  the  object 
of  his  search  has  been  attained.  As  a  matter  of  fact, 
the  key  is  intended  simply  to  lead  him  by  the  quickest 
method  to  a  thorough  study  of  the  substance. 

The  key  in  the  following  pages  consists  of  a  series 
of  tables  1  in  two  divisions.  The  first  includes  those 
minerals  that  have  a  metallic  luster,  and  a  few  which 
might  be  confused  with  these.  Minerals  with  a  metal- 
lic luster  are  opaque  in  their  thinnest  edges.  Most 
of  them  give  a  black  or  dark-colored  streak.  The 
second  division  includes  the  remaining  minerals, 
i.e.,  those  with  a  non-metallic  luster.  These  are  trans- 
parent in  very  thin  splinters  and  upon  their  thin  edges, 
and  most  of  them  give  a  colorless  or  light-colored 
streak.  The  sub-divisions  are  based  on  color  of 
streak,  color  in  reflected  light  and  hardness. 

In  testing  for  hardness,  it  is  important  to  know 
that  the  scratching  substance  will  actually  scratch 

1  The  names  of  a  few  minerals  are  included  in  the  tables,  although 
the  minerals  are  not  described  in  the  text.  In  these  cases,  there  are, 
naturally,  no  reference  numbers. 

168 


KEY  TO  DETERMINATION  OF  MINERALS        169 

the  substance  being  tested,  and  also  that  the  latter 
will  not  scratch  the  former.  Further,  it  is  likewise 
important  that  the  scratching  substance  be  clean 
and  fresh.  If  a  cent  or  a  knife  blade  is  being  used 
for  scratching,  they  should  be  bright;  if  a  mineral, 
it  should  not  be  coated  with  a  tarnish  or  a  weathered 
layer. 

It  is  convenient  to  remember  that  minerals  with  a 
hardness  of  less  than  2.5  will  leave  a  mark  on  paper; 
those  with  a  hardness  of  less  than  3.5  can  be  scratched 
by  a  cent;  those  with  a  hardness  of  less  than  5.5  can 
be  scratched  by  a  good  knife  blade;  and  those  with  a 
hardness  of  less  than  7  can  be  scratched  by  quartz. 

It  is  also  to  be  remembered  that  the  color  of  a 
mineral  is  its  color  on  a  fresh  fracture  and  not  on  a 
weathered  surface. 

The  tables  in  this  book  are  intended  to  serve  as  a 
guide  to  the  sections  in  which  the  minerals  are  de- 
scribed. Recourse  must  be  had  to  the  description 
before  the  nature  of  the  substance  being  studied  can 
be  established. 


170 


MINERALS  AND  ROCKS 


A.     MINERALS   WITH   METALLIC   LUSTER1 

STREAK  BLACK  OR  DARK  GRAY 


Color. 

Name. 

Hard- 
ness. 

Ref. 
No. 

Name. 

Hard- 
ness. 

Ref. 
No. 

White  or 

Stibnite 

2-2  5 

7 

Smaltite 

5  5 

21 

Light 

Galena 

2  5 

9 

Arsenopyrite  . 

5  5-6 

22 

Gray 

Cobaltite  .... 

5.5 

20 

Marcasite.  .  .  . 

6-6.5 

15 

Brassy 
Bronze 

Bornite  
Chalcopyrite  . 
Pyrrhotite.  .  . 

3-3.5 
3.5-4 
3.5-4.5 

18 
17 
16 

Niccolite  
Pyrite  
Marcasite.  .  .  . 

5.5 
5-6.5 
6-6.5 

19 
14 
15 

Molybdenite  . 
Graphite  
Pyrolusite 

1-1.5 
1-1.5 
1-2 

8 
2 
41 

Staurolite.  .  .  . 
Wolframite.  .  . 
Ilmenite 

4 
5-5.5 
5-6 

93 
69 
132 

Dark 

Wad  

1-2.5 

MnO2 

Magnetite.  .  .  . 

5.5-6.5 

47 

Gray 
or 

Stibnite 

2-2  5 

+Aq- 

7 

Franklinite.  .  . 
Columbite  .  . 

5.5-6.5 
6-6.5 

49 
79 

Black 

Galena  
Chalcocite.  .  . 
Tetrahedrite  . 
Uraninite  .... 

-2.5 
2.5-3 
3-4 
3-5.5 

9 
11 
25 

84 

Tantalite  .... 
Corundum  .  .  . 

6-6.5 

7-9 

80 
37 

Blue 

Covellite  

1.5-2 

12 

Brown 

Wad  

1-3 

MnO2 

+Aq. 

STREAK  RED 


Wad.  .  .  .  

1-3 

MnO2 

Cuprite  

3.5-4 

35 

Dark 

Gray 

Hematite  .... 
Copper 

2-3 
2.5-3 

+Aq. 

38 
4 

Wolframite.  .  . 
Samarskite.  .  . 

5-5.5 
5-6 

69 
81 

or 
Black 

Pyrargyrite.  .. 
Tetrahedrite  . 

2.5-3 
3-4 

24 
25 

Franklinite.  .  . 
Hematite  .... 
Columbite.  .  . 

5  .  5-6  .  5 
6-6.5 
6-6.5 

49 
38 
79 

Brown 

Wad  
Hematite  .... 

1-3 
2-3 

Mn02 

+Aq. 

38 

Wolframite.  .  . 

5-5.5 

69 

Hematite  .... 
Cinnabar 

2-3 
2-2  5 

38 
13 

Copper  
Gold  

2.5-3 
2.5-3 

4 
6 

Red 

Proustite  .  .  .  . 
Pyrargyrite  .  . 

2.5 
2.5-3 

23 

24 

Hematite  .... 

3-6 

38 

1Where  no  reference  number  is  given,  the  mineral  is  not  described  in  the  text. 
Its  composition  is  indicated  for  the  purpose  of  identification. 


KEY  TO  DETEEMINATION  OF  MINERALS        171 


A.    MINERALS  WITH  METALLIC  LUSTER— Continued 

STREAK  YELLOW 


Color. 

Name. 

Hard- 
ness. 

Ref. 
No. 

Name. 

Hard- 
ness. 

Ref. 
No. 

Siderite. 

3  5-4 

53 

Samarskite. 

5-6 

81 

Dark 
Gray 

Sphalerite.  .  .  . 
Limonite  

3.5-4 
5-5.5 

10 
45 

Brookite  
Rutile  '.. 

5.5-6 
6-7 

39 
39 

or 

T^laolr 

Huebnerite.  .  . 

5-5.5 

69 

Cassiterite.  .  . 

6-7 

40 

Hornblende.  . 

5-6 

116 

Limonite  

1-5.5 

45 

Limonite  

5-5.5 

45 

Brown 

Sphalerite.  .  .  . 
Zincite  

3.5-4 
4-4.5 

10 
36 

Brookite  
Rutile  

5.5-6 
6-7 

39 
39 

Huebnerite.  .  . 

4.5-5.5 

69 

Cassiterite.  .  . 

6-7 

40 

Limonite  

1.5-5 

45 

Huebnerite.  .  . 

4.5-5 

69 

Yellow 

Gold  

2.5-3 

6 

Limonite  

5-5.5 

45 

Sphalerite.  .  .  . 

3.5-4 

10 

Cassiterite.  .  . 

6-7 

40 

Sphalerite.  .  .  . 

3  5-4 

10 

Brookite.  .  .  . 

5.5-6 

39 

Red 

Zincite  

4-4.5 

36 

Rutile  

6-7 

39 

STREAK    BROWN 


1 

Wad 

1-3 

Mn02 

Dark 
Gray 
or 

Hematite  .... 
Tetrahedrite  . 
Uraninite.  .  .  . 
Siderite  
Sphalerite.  .  .  . 
Cuprite. 

2-3 
3-4 
3.5-5 
3.5-4 
3.5-4 
3  5-4 

+Aq. 

38 
25 
84 
53 
10 
35 

Samarskite.  .  . 
Chromite.  .  .  . 
i  Brookite  
Franklinite.  .  . 
Hematite.  .  .  . 
Columbite.  .  . 
Tantalite 

5-6 
5.5 
5.5-6 
5.5-6.5 
6-6.5 
6-6.5 
6-6  5 

81 
48 
39 
49 
38 
79 
80 

Black 

Limonite  
Huebnerite.  .  . 
Wolframite. 

4.5-5.5 
5-5.5 
5-6 

45 
69 
69 

Rutile  
Cassiterite  .  .  . 
Spinel 

6-7 
6-7 

7  5-8 

39 
40 
46 

Hornblende.  . 
Ilmenite  

5-6 
5-6 

116 
132 

Corundum.  .  . 

7-9 

37 

Brown 

Wad  

Hematite  .... 
Limonite  
Siderite  

1-3 

1-6 
1-5.5 
3.5-4 

Mn02 
+Aq. 
38 

45 
53 

Ilmenite  
Brookite  
Franklinite.  .  . 
Columbite.  .  . 
Rutile  

5-6 
5.5-6 
5.5-6.5 
6-6.5 
6-7 

132 
39 
49 
79 
39 

Sphalerite.  .  .  . 
Uraninite  .... 

3.5-4 
3.5-5 

10 
84 

Cassiterite.  .  . 
Spinel  

6-7 

7  5-8 

40 
46 

Huebnerite.  .  . 
Wolframite.  .  . 

4  .  5-5  .  5 
5-6 

69 
69 

172 


MINERALS  AND  ROCKS 


A.     MINERALS  WITH   METALLIC  LUSTER— Continued 
STREAK  BROWN — Continued 


Color. 

Name. 

Hard- 
ness. 

Ref. 
No. 

Name. 

Hard- 
ness. 

Ref. 
No. 

Yellow 

Limonite  .... 
Siderite  
Sphalerite. 

1-5.5 
3.5-4 
3  5-4 

45 
53 
10 

Huebnerite.  .  . 
Cassiterite  .  .  . 
Spinel 

4.5-5.5 
6-7 

7  5-8 

69 
40 
46 

Red 

Cinnabar.  .  .  . 
Cuprite  

2-2.5 
3.5-4 

13 
35 

Rutile  

6-7 

39 

STREAK   GREEN 


Uraninite 

3-5  5 

84 

Augite. 

5-6 

111 

Green 

Hornblende  .  . 

5-6 

116 

Spinel  

7.5-8 

46 

Brown  or 
Red 

Uraninite  .... 

3-5.5 

84 

Huebnerite.  .  . 

4.5-5.5 

69 

STREAK    GRAY 


Silver- 

Silver 

2  5-3 

5 

Platinum  .  .  . 

4-5 

Pt 

\\  hite 

Antimony.  .  .  . 

3-4 

Sb 

Dark 

Gray  or 
Black 

Molybdenite  . 
Graphite  
Silver  
Biotite  
Sphalerite. 

1-1.5 
1-2 
2.5-3 
2.5-3 
3  5-4 

8 
2 
5 
95 
10 

Hornblende.  . 
Augite  
Hypersthene  . 
Brookite  
Rutile  .  ... 

5-6 
5-6 
5-6 
5.5-6 
6-7 

116 
111 
110 
39 
39 

Titanite 

5-5  5 

131 

Spinel  

6-7 

46 

Huebnerite.  .  . 

5-5.5 

69 

Brown 

Huebnerite.  .  . 
Brookite  

5-5.5 
5.5-6 

69 
39 

Rutile  
Cassiterite  .  .  . 

6-7 
6-7 

39 
40 

STREAK   WHITE 


Silver- 

Silver  

2.5-3 

5 

Antimony.  .  .  . 

3-4 

Sb 

white 

Biotite  

2  5-3 

95 

Hypersthene  . 

5-6 

110 

Dark 

Gray 
o  r 
Black 

Silver  
Titanite  
Hornblende.  . 
Augite. 

2.5-3 
5-5.5 
5-6 
5-6 

5 
131 
116 
111 

Cassiterite.  .  . 
Garnet  
Tourmaline  .  . 
Spinel 

6-7 
6.5-7 

7-7.5' 
7  5-8 

40 

88 
108 
46 

Brown 

Cassiterite.  .  . 

6-7 

40 

KEY  TO  DETERMINATION  OF  MINERALS        173 


B.     MINERALS   WITH   NON-METALLIC   LUSTER 

STREAK  DARK  GRAY  OR  BLACK 


Color. 

Name. 

Hard- 
ness. 

Ref. 
No. 

Name. 

Hard- 
ness. 

Ref. 

No. 

Graphite  

1-2 

2 

Psilomelane  l  . 

5-6 

Mn- 

Gray  or 
Black 

Wad  
Wolframite.  .  . 

1-3 
5-5.5 

MnO2 
+Aq. 

69 

Corundum  .  .  . 

7-9 

Ba-K 
37 

Brown 

Wad  

1-3 

MnO2 
+Aq. 

STREAK  BROWN 


Wad  

1-3 

MnO2 

Dark 
Gray 
or 
Black 

Uraninite  .... 
Siderite  
Sphalerite.  .  .  . 
Cuprite  
Goethite 

3-5.5 
3.5-4 
3.5-4 
3.5-4 
4  5-5  5 

+Aq. 

84 
53 
10 
35 
45 

Hornblende  .  . 
Psilomelane.  . 

Chromite  .... 
Brookite.  .... 
Rutile 

5-o 
5-6 

5-6 
5.5-6 
6-7 

Mn- 
Ba-K 
48 
39 
39 

Ferberite  .... 
Wolframite.  .  . 

4.5-5 
5-5.5 

69 
69 

Cassiterite  .  .  . 
Spinel  

6-7 

7.5-8 

40 
46 

Wad 

1-3 

MnO2 

Goethite  

4.5-5 

45 

Hematite  
Limonite  
Bauxite  

1-3 
1-3 
1-3 

+  Aq. 
38 

45 
44 

Huebnerite.  .  . 
Wolframite.  .  . 
Hornblende.  . 
Brookite. 

4.5-5 
5-5.5 
5-6 
5  5-6 

69 
69 
116 
39 

Brown 

Cinnabar.  .  .  . 

2-2.5 

13 

Rutile 

6-7 

39 

Chrysocolla  .  . 
Uraninite  .... 
Siderite  
Sphalerite.  .  .  . 

2-4 
3-5.5 
3.5-4 
3.5-4 

121 
84 
53 
10 

Cassiterite.  .  . 
Spinel  

6-7 

7.5-8 

40 
46 

Red 

Hematite  .... 
Cinnabar.  .  .  . 
Hematite  .... 
Cuprite  
Sphalerite.  .  .  . 

1-3 
2-2.5 
3-6 
3.5-4 
3.5-4 

38 
13 
38 
35 
10 

Huebnerite.  .  . 
Wolframite.  .  . 
Rutile  
Cassiterite  .  .  . 

4.5-5 
5-5.5 
6-6.5 
6-7 

69 
69 
39 
40 

Yellow 

Bauxite  
Limonite  

1-3 
1-3 

44 

45 

Goethite  

4-5.5 

45 

1  The  composition  of  psilomelane  is  doubtful.     The  mineral  contains  the  three 
elements  indicated. 


174 


MINERALS  AND  ROCKS 


B.     MINERALS  WITH  NON-METALLIC   LUSTER— Continued 

STREAK   RED 


Color. 

Name. 

Hard- 

Ref. 

Name. 

Hard- 

Ref. 

ness. 

No. 

ness. 

No. 

Dark 

Gray  or 

Hematite.  .  .  . 

1-3 

38 

Cuprite. 

3  5-4 

35 

Black 

Brown 

Cinnabar.  .  .  . 

2-2.5 

13 

Hematite  .... 

3-6 

38 

Bauxite  
Hematite  .... 

1-3 
1-3 

44 

38 

Pyrarygrite.  . 
Crocoite  

2.5-3 
2.5-3 

24 
71 

Red 

Ery  thrite  .... 

1.5-2 

77 

Zincite  

4^.5 

36 

Cinnabar.  .  .  . 

2-2.5 

13 

Wolframite.  .  . 

5-5.5 

69 

Proustite.  .  .  . 

2-5 

23 

Yellow 

Hematite  .... 

3-6 

38 

STREAK    YELLOW 


Dark 

Siderite 

3  5-4 

53 

Rutile 

6-7 

39 

Gray  or 

Huebnerite.  .  . 

4.5-5.5 

69 

Cassiterite  .  .  . 

6-7 

40 

Black 

Brookite  

5.5-6 

39 

Wad  

1-3 

Mn02 

Huebnerite.  .  . 

4.5-5.5 

69 

Brown 

Limonite  
Bauxite  
Siderite  

1-3 
1-3 
3.5-4 

+Aq. 

45 

44 
53 

Brookite  
Rutile  
Cassiterite.  .  . 

5.5-6 
6-6.5 
6-7 

39 
39 
40 

Sphalerite.  .  .  . 

3.5-4 

10 

Bauxite 

1-3 

44 

Zincite 

4-4  5 

36 

Wulfenite.  .  .  . 

3 

70 

Huebnerite.  .  . 

4.5-5.5 

69 

Red 

Vanadinite.  .  . 

3 

75 

Rutile  

6-6.5 

39 

Sphalerite.  .  .  . 

3.5-4 

10 

Cassiterite  .  .  . 

6-7 

40 

Bauxite  

1-3 

44 

Vanadinite.  .  . 

3 

75 

Limonite  

1-3 

45 

Pyromorphite 

3.5-4 

73 

Vo11/-vnr 

Sulphur 

1  5-2 

3 

Sphalerite. 

3  5-4 

10 

i  enow 

Carnotite 

2-3 

83 

Zincite  

4-4.5 

36 

Wulfenite.  .  .  . 

3 

70 

STREAK    ORANGE 

Red 

Crocoite 

2-5 

71 

Zincite  

4-4.5 

36 

KEY  TO  DETEEMINATION  OF  MINERALS        175 


B.     MINERALS  WITH  NON-METALLIC  LUSTER— Continued 


STREAK  GREEN 


Color. 

Name. 

Hard- 
ness. 

Ref. 
No. 

Name. 

Hard- 
ness. 

Ref. 
No. 

Dark 
Gray 
or 

Uraninite.  .  . 
Augite.  . 

3-3.5 
5-6 

84 
111 

Spinel  

7.5-8 

46 

Black 

Green 

Glauconite.  . 
Chlorites..  .  . 
Chrysocolla. 

1-2 
1-2.5 
2-3 

* 

100 
121 

Pyromorphite 
Hornblende.  . 
Augite. 

3.5-4 
5-6 
5-6 

73 

116 
111 

Atacamite.  . 
Malachite..  . 

3-3.5 
3.5-4 

Cu2(OH)3Cl 
60 

Turquois  
Chloritoid.  .  .  . 

6 
6-7 

78 
99 

STREAK  BLUE 


Vivianite 

1  5-2 

Fe3(P04)2-8H20 

Azurite. 

3.5-4 

61 

Blue 

Chrysocolla. 

2-3 

121 

Glaucophane. 

6-6.5 

117 

Green 

Crocidolite  . 

4 

NaFe(Fe,Mg)(Si03)3 

STREAK   WHITE 


Gypsum  

1.5-2 

67 

Yttrotantalite 

5-5.5 

82 

Halite  

2-2.5 

27 

Hornblende.  . 

5-6 

116 

Apatite  

2-5 

72 

Augite  

5-6 

111 

Biotite  

2-5 

95 

Hypersthene. 

5-6 

110 

Calcite  

3 

50 

Octahedrite.  . 

5.5-6 

39 

Anhydrite.... 

3-3.5 

62 

Brookite  

5.5-6 

39 

T~"v         1 

Cerussite.  .  .  . 

3-3.5 

59 

Labradorite.  . 

6-6.5 

120 

Dark 
Gray 

Serpentine..  . 
Wavellite...  . 

3-4 
3.5-4 

104 
76 

Epidote  
Chloritoid..  .  . 

6-7 
6-7 

92 
99 

or 
Black 

Ankerite  
Dolomite..  .  . 

3.5-4 
3.5-4 

Ca(M&,Fe)(COs)2 

51 

Rutile  
Cassiterite.  .  . 

6-7 
6-7 

39 
40 

Sphalerite.... 

3.5-4 

10 

Garnet  

6.5-7.5 

88 

Magnesite  .  . 

3.5-5 

52 

Quartz  

7 

34 

Fluorite  .... 

4 

29 

Tourmaline  .. 

7-7.5 

108 

Huebnerite.  . 

4.5-5.5 

69 

Staurolite..  .  . 

7-7.5 

93 

Titanite  .... 

5-5.5 

131 

Spinel  

7.5-8 

46 

Glaucophane 

5-5.5 

117 

Diamond.  .  . 

10 

1 

*  Hydrous  silicate  of  K  and  Fe. 


176 


MINERALS  AND  EOCKS 


B.     MINERALS  WITH  NON-METALLIC  LUSTER— Continued 
STREAK  WHITE — Continued 


Color. 

Name. 

Hard- 
ness. 

Ref. 
No. 

Name. 

Hard- 
ness. 

No. 
Ref. 

Cerargyrite  .  . 
Tripolite 

1-1.5 
1-2  5 

26 

Si02 

Chabazite.  .  .  . 
Harmotome 

4-5 
4-5 

128 
124 

Kaolin  ite. 
Gypsum  
Halite 

1-2.5 
1.5-2 
2-2.5 

106 

67 

27 

Apatite  
Calamine 
Huebnerite 

4.5-5 
4.5-5 
4  5-5 

72 
107 
69 

Muscovite.  .  . 
Phlogopite  .  .  . 
Apatite  
Biotite  
Chrysotile  .  .. 
Barite  

2-3 
2-3 
2-3 
2.5-3 
2.5-3 
2.5-3.5 

96 
95 

72 
95 
104 
63 

Smithsonite.  .  . 
Titanite  
Nephelite 
Enstatite  .... 
Bronzite  
Hypersthene  . 

5 
5-5.5 
5-6 
5-6 
5-6 
5-6 

54 
131 
94 
110 
110 
110 

Vanadinite.  .  . 
Wulfenite. 

3 
3 

75 
70 

Hornblende.  . 
Augite 

5-6 
5-6 

116 
111 

Calcite 

3 

50 

Willemite 

5-6 

86 

Brown 

Anglesite  .... 
Serpentine 

3-3.5 
3-4 

65 
104 

Troostite.  .  .  . 
Opal 

5-6 
5  5-6 

87 
42 

Stilbite  
Laumontite.  . 
Apatite  
Dolomite.  .  .  . 

3-4 
3-4 
3.5 
3.5-4 

125 
126 

72 
51 

Octahedrite.  . 
Brookite  
Epidote  
Rutile  

5.5-6 
5.5-6 
6-7 
6-7 

39 
39 
92 
39 

Sphalerite.  .  .  . 
Wavellite  .... 
Aragonite. 

3.5-4 
3.5-4 
3.5-4 

10 
76 
56 

Cassiterite  .  .  . 
Vesuvianite.  . 
Olivine 

6-7 

6.5 
6  5-7 

40 
109 

85 

Strontianife 

3  .  5-4 

57 

Garnet  .  . 

6.5-7  5 

88 

Siderite  
Pyromorphite 
Mimetite  .... 
Rhodochrosite 

3.5-4 
3.5-4 
3.5-4 
3.5-4 

53 

73 

74 
55 

Quartz  
Tourmaline  .  . 
Staurolite.  .  .  . 
Zircon 

7 
7-7.5 

7-7.5 
7  5 

34 
108 
93 
89 

Magnesite.  .  . 
Fluorite  
Clintonite*.  .  . 

3.5-5 
4 
4-5 

52 

29 
99 

Spinel  
Corundum  .  .  . 
Diamond.  .  .  . 

7.5-8 
9 
10 

46 
37 
1 

Cerargyrite  .  . 
Glauconite  .  .  . 
Kaolinite 

1-1.5 
1-2 
1-2  5 

26 
106 

Wulfenite  
Anglesite  
Stilbite  . 

3 
3-3.5 
3-4 

70 
65 
125 

Talc. 

1-2.5 

105 

Serpentine..  . 

3-4 

104 

Chlorites. 

1-2.5 

100 

Wavellite  .... 

3.5-4 

76 

Halite 

2-2.5 

27 

Aragonite  .... 

3.5-4 

56 

Green 

Brucite  
Actinolite  .... 
Chrysocolla.  . 
Chrysotile  .  .  . 
Phlogopite.  .  . 
Biotite  ...... 

2-2.5 
2-3 
2-3 
2.5-3 
2.5-3 
2.5-3 

43 
114 
121 
104 
95 
95 

Strontianite  .  . 
Pyromorphite. 
Rhodochrosite. 
Fluorite  
Scheelite  
Apatite  

3.5-4 
3.5-4 
3.5-4.5 
4 
4-5 
4.5-5 

57 
73 
55 
29 
68 
72 

Barite  

2.5-3 

63 

Calamine.  .  .  . 

4.5-5 

107 

*A  calcium-bearing  brittle  mica. 


t  Hydrous  silicate  of  K  and  Fe. 


KEY  TO  DETERMINATION  OF  MINERALS        177 


B.     MINERALS  WITH  NON-METALLIC  LUSTER— Continued 
STREAK  WHITE — Continued 


Color. 

Name. 

Hard- 

Ref. 

Name. 

Hard- 

Ref. 

ness. 

No. 

ness. 

No. 

Smithsonite  . 

5  * 

54 

Microcline  . 

6-6.5 

119 

Titanite.  .  .  . 

5-5.5 

131 

Epidote...  .  . 

6-7 

92 

Hornblende  . 

5-6 

116 

Chloritoid... 

6-7 

99 

Augite  

5-6 

111 

Vesuvianite 

6.5 

109 

Hypersthene 

5-6 

110 

Olivine  

6.5-7 

85 

Nephelite.  .  . 

5-6 

94 

Garnet.  .  .  . 

6.5-7.5 

88 

Green 

Actinolite.  .  . 

5-6 

114 

Quartz  .... 

7 

34 

Enstatite.  .  . 

5-6 

110 

Tourmaline 

7-7.5 

108 

Bronzite  .... 

5-6 

170 

Spinel  

7.5-8 

46 

Willemite.  .  . 

5-6 

86 

Beryl  

7.5-8 

103 

Opal  

5-6 

42 

Topaz  

8 

91 

Turquoise.  .  . 

6 

78 

Corundum. 

9 

37 

Labradorite  . 

6-6.5 

120 

Laumontite  . 

1-1-2 

126 

Fowlerite.  . 

5-6 

(Mn,Zn)SiO» 

Gypsum  .... 

1.5-2 

67 

Willemite  .  . 

5-6 

86 

Lepidolite.  .  . 

2-4 

98 

Rhodonite  . 

5.5-6.5 

MnSiOs 

Calcite  

3 

50 

Tephroite.  . 

6 

Mn2SiO4 

Laumontite  . 

3-4 

126 

Orthoclase  . 

6-6.5 

118 

Pink 

Dolomite.  .  . 
Alunite  

3.5-4 
3.5-4 

51 
66 

Epidote.  .  .  . 
Andalusite  . 

6-7 
6-7.5 

92 
90 

Rhodochro-  . 

Garnet.  .  .  . 

6.5-7 

88 

site  

3.5-4.5 

55 

Tourmaline 

7-7.5 

108 

Fluorite  .... 

4 

29 

Topaz  

8 

91 

Apophyllite  . 

4.5-5 

122 

Spinel  

8 

46 

Tremolite.  .  . 

5-6 

113 

Corundum  . 

9 

37 

Cerargyrite.  . 

1-1.5 

26 

Stilbite  

3-4 

125 

Carnallite.  .  . 

1-2 

* 

Laumontite 

3-4 

126 

Kaolinite  .  .  . 

1-2.5 

106 

Serpentine  . 

3-4 

104 

Talc  

1-2.5 

105 

Wavellite  .  . 

3.5-^: 

76 

Gypsum  .... 

1.5-2 

67 

Dolomite.  . 

3.5-4 

51 

Sulphur  

1.5-2.5 

3 

Aragonite.  . 

3.5-4 

56 

Sylvite  

2-2.5 

28 

Strontianite 

3.5-4 

57 

Halite  

2-2.5 

27 

Sphalerite.  . 

3.5-4 

10 

Yellow 

Muscovite.  .  . 
Phlogopite  .  . 

2-3 
2-3 

96 
95 

Pyr  o  m  o  r- 

phite.  .  .  . 

3.5-4 

73 

Chrysotile  .  . 

2.5-3 

104 

Mimetite.  . 

3.5-4 

74 

Barite  

2.5-3.5 

63 

Rhodochro- 

Calcite  

3 

50 

site  

3.5-4.5 

55 

Wulfenite.  .  . 

3 

70 

Magnesite  . 

3.5-5 

52 

Vanadinite.  . 

3 

75 

Fluorite.  .  . 

3.5-5 

29 

Celestite.  .  .  . 

3-3.5 

64 

Chabazite.  . 

^5 

128 

Anglesite  .  .  . 

3-3.5 

65 

Harmotome 

4-5 

124 

Cerussite.  . 

3-3.5 

59 

Phillipsite.  . 

4-5 

123 

KMgCl3-6H2O 


178 


MINKRALS  ANO   HOCKS 


B.     MINERALS  WITH  NON-METALLIC  LUSTER— Continued 
STREAK  WHITE — Continued 


Color. 

Name. 

Hard- 

noss. 

Ref.  . 

No.    ' 

Name. 

Hard- 

1\.'SS. 

K,-f 
MQ 

Scheelite  
Apatite  

4.5 
4.5-5 

68 

7-J 

Orthoclnso 

I'.pidotc 

6-6.5 

(>  7 

118 
02 

Yellow 

Calamine  .... 
Huobnorite.  .  . 
Sniithsonito  .  . 
Xatrolito.  .  .  . 
Tit-anito        .  . 

4.5-5 
4.5-5 
5 
5-5.5 
5-5.5 

107 
89 
M 
129 
LSI 

\'osuvi;uiiti 
(iarnet.  ,  .  . 
Quart!.  .  .  . 
Tourmalins 
Zircon. 

6-7 
6.5-7.5 
7 
7-7.5 
7.5 

100 

ss 
34 

IDS 

so 

\epholito    .  .  . 

;>  i» 

M 

IVrvl  

7-8 

IMS 

1'  nstat  ito  .... 

;>  (i 

110 

Sj-inel  

7  o  S 

U> 

\\illemite.  .  .  . 

:>  (\ 

86 

'I'oraz  

S 

91 

Opal 

5  ;>  r> 

42 

Corundum 

o 

37 

Kaolin  ito.  .  .. 
Talc  

1-2.T) 
l-2.o 

106 
105 

Sduvlito.. 
.\i>ophvllito. 

4.5-5 
4  5-5 

68 

,00 

kaumonlito.. 
GSvrxsum   . 

1^3 
1.5-2 

L26 

07 

Apatiti\. 
1  luclmtM-itr.. 

•i  o  :> 
4.5-5.5 

72 
60 

Sylvite   

2S 

Aualcite.  .  .  . 

;>  ;>  ;> 

130 

rfalite  

27 

Natrolite.  .  . 

1'*) 

Phlogopite.  .. 

Calrito 

•j  :.  s 
3 

M 

;x^ 

Titanittv. 
Nephelite, 

5-6 

131 
M 

\YultVnitiv 
\  Mivulinite. 

3 
;^ 

70 
75 

WllUMnitO..   . 

Opal    . 

5-6 
5-6 

SO 
42 

Red 

Anhydrite, 

CVlostito  
Barite 

3-3.5 
3-3.5 
3-3.5 

(>2 

(\\ 
(K 

Orthoolaso. 
Kpulote  
KNitilo  

(\  (\  :> 
6-7 
6-7 

118 
02 
30 

Stilhito 

3-4 

12,-) 

C\assitoritt\ 

(i  7 

40 

1  'Uimont  it  o 

3—  i 

126 

Olivino  . 

6  5-7 

v--, 

Sorpout  um 

3-4 

HH 

Garnet  . 

6  5-7  5 

ss 

Dolomite  .... 
Aragonite..  ,  . 
\nkerito 

3.5-4 
3.5-4 
3  5-4 

51 
56 

Ca(Mir  F«KCO))t 

C>u:\rtx  

Tourmaline, 

Xircon  

7 

7-7.5 
7.5 

34 

HIS 
S«) 

Sph&terite 

3.5-4 

10 

Spinol  

7.5-8 

40 

Ixhodoi'hrositc 

;>  ;>  i 

5o 

Topaz  

S 

91 

Chabaiita 

Harmotomo.  . 

4-5 
4-5 

12S 
124 

Corundum.  . 

9 

87 

Kaolin. 

1-2.5 

106 

Andi'sito. 

3-3.5 

ti;> 

s\lvite 

2S 

Amgonite.  .  . 

;i  :>  i 

;xi 

Halite  

2-2.5 

27 

\\avollito. 

3.5-4 

re 

Hruoite  

2-2.5 

43 

Kluoriio      . 

4 

20 

Blue 

Chrvsocolla.  . 
Barite 

2-4 
2.5-3.5 

121 
63 

Apatito  
Calamino. 

-1  .-i  .-i 

•\  ;»  o 

72 
107 

Caleito 

3 

50 

Smithsonito. 

5 

54 

Colostite. 

;;  ;;  ;. 

64 

Nopliolito. 

5-6 

0-1 

! 

KEY  TO  DETERMINATION  OF  MINERALS        179 


B.    MINERALS  WITH  NON-METALLIC   LUSTER— Continued , 
STREAK  WHITE — Continued 


Color. 

Name. 

Hard- 
ness. 

Ref. 
No. 

Name 

Hard- 
ness. 

Ref. 

No. 

~108~ 
103 
46 
91 
37 

Blue 

Opal. 

5.5-6 
6 
6-6.5 

0-7 
7 

42 
78 
117 
109 
34 

Tourmaline  .  .  . 
Beryl  

7-7.5 

7  s 
7.5-8 
8 
9 

Turquoise..  .  . 
Glaucophane  . 
Vesuvianite  .  . 
Quartz 

Spinel 

Topaz 

Corundum  .... 

Purple 

Halite     .      .  . 

2-2.5 
3 
4 
4.5-5 
5-6 

27 
50 
29 
72 
113 

Quartz  

7 
8 
8 
9 

34 
91 
46 
37 

Calcite 

Topaz 

Fluorite  

Spinel  

Apatite  

Corufidum.  .  .  . 

Tremolite.  .  .  . 

Bronze 

Phlogopite  .  .  . 

2.5-3 

95 

I   ran.ci' 

^"hito  or 
Light 
Gray 

; 

Yanailiniio..   . 

3 

75 

Spinel  

8 

46 

(.  Vrargyrite  .  . 
Calc'ito 

1-1.5 
1-2.5 
1-2.5 
1-2.5 
1-3 
1.5-2 
1.5-2 
1.5-2 
2-2.5 
2-2  5 
2-3 
2-3 
2-4 
2-5 
2.5-3 
2.5-3 
3 
3 
^-3.5 
3-3.5 
3-3.5 
3-4 
3-4 
3-6 
3.5-4 
3.5-4 
3.5-4 
3.5-4 

26 
50 
105 
43 
44 
30 
31 
67 
28 
27 
96 
97 
98 
72 
104 
63 
50 
70 
64 
65 
59 
125 
126 
90 
76 
51 
58 
56 

Strontianite  .  . 
Siderite.  . 

3.5-4 
3.5-4 
3.5-4 
3.5-4 
3.5-4 
3.5-4 
3.5-4.5 
3.5-4.5 
4 
4 
4-5 
4-5 
4-5 
4-5 
4-5 
4-5 
4-5 
4.5-5 
4.5-5 
5 
5-5.5 
5-5.5 
5-5.5 
5-6 
5-6 
5-6 
5-6 
5-6 

57 

53 

* 

66 
73 
74 
55 

52  • 
29 

CaSiOi 

33 
128 
122 
124 
123 
68 
102 
72 
107 
54 
130 
129 
127 
94 
113 
110 
115 
86 

Talc  

Ankerite.  . 

Brucite 

Alunite  
Pyromorphite 
Mimetite.  .  .  . 
Rhodochrosi  te 
Magnesite  .  .  . 
Fluorite  
Wollastonite  . 
Colemanite.  .  . 
Chabazite.  .  .  . 
Apophyllite.  . 
Harmotome.  . 
Phillipsite  
Scheelite  
Kyanite 

Bauxite 

Niter 

Soda-niter  .  .  . 
Gvspum  .  . 

Sylvite  

Halite  

Muscovite.  .  . 
Paragonite.  .  . 
Lepidolite.  .  .  . 
Apatite  

rhrvsotile  ..  . 
Ha  rite     .... 

Calcite  

Wulfenite.  .  .  . 
Celestite. 

Apatite. 

Calamine  .... 
Smithsonite  .  . 
Analcite 

Anglesite.  .  .  . 
Cerussite.  .  .  . 
Stilbite  

Natrolite.  .  .  . 
Scolecite  
Nephelite.  ..  . 
Tremolite.  .  .  . 
Enstatite  .... 
Asbestus  
Willemite  

Laumontite.  . 
Andalusite.  .  . 

Wavcllite  
Dolomite.  .  . 
Witherite  
Aragonite..  .  . 

*Ca(Mg,Fe)(COi)j. 


180 


MINERALS  AND  ROCKS 


B.     MINERALS  WITH  NON-METALLIC   LUSTER— Continued 
STREAK  WHITE — Continued 


Color. 

Name. 

Hard- 
ness. 

Ref. 
No. 

Name. 

Hard- 
ness. 

Ref. 

No. 

Opal 

5  5-6 

42 

Tourmaline 

7-7  5 

108 

White 

Leucite 

5  5-6 

101 

Zircon. 

7  5 

89 

or 

Orthoclase 

6-6  5 

118 

Beryl.     .  .    . 

7-8 

103 

Light 
Gray 

Microcline.  .  . 
Plagioclase.  .  . 
Garnet  
Quartz  

6-6.5 
6-6.5 
3.5-7.5 

7 

119 
120 

88 
34 

Topaz  
Corundum.  .  . 
Diamond  ... 

8 
9 
10 

91 
37 

1 

VI 


LIST  OF  MINERALS  ARRANGED  ACCORDING 
THEIR   IMPORTANT  CONSTITUENTS 


TO 


Albite  (120) 
Alunite  (66) 
Andalusite  (90) 
Anorthite  (120) 
Augite  (111) 
Bauxite  (44) 
Beryl  (103) 
Brittle  micas  (99) 
Corundum  (37) 
Cyanite  (102) 


ALUMINIUM 

Garnet  (88) 
Glaucophane  (117) 
Hornblende  (116) 
Kaolinite  (106) 
Kyanitc  (102) 
Leucite  (101) 
Micas  (95-100) 
Microcline  (119) 
Nephelite  (94) 
Orthoclase  (118) 


Spinel  (46) 
Spodumene  (112) 
Staurolite  (93) 
Topaz  (91) 
Tourmaline  (108) 
Turquoise  (78) 
Vesuvianite  (109) 
Wavellite  (76) 
Zeolites  (123-130) 


Pyrargyrite  (24) 


ANTIMONY 

Stibnite  (7) 


Tetrahedrite  (25) 


Arsenopyrite  (22) 
Cobaltite  (20) 
Erythrite  (77) 


ARSENIC 


Mimetite  (74) 
Niccolite  (19) 
Proustite  (23) 


Smaltite  (21) 
Tetrahedrite  (25) 


Barite  (63) 
Harmotome  (124) 


Beryl  (103) 


Borax  (32) 


BARIUM 

Psilomelane  (173) 

BERYLLIUM 
BORON 

Colemanite  (33) 
181 


Witherite  (58) 


Tourmaline  (108) 


182 


MINERALS  AND  ROCKS 


Actinolite  (114) 
Andradite  (88) 
Anhydrite  (62) 
Anorthite  (120) 
Apatite  (72) 
Apophyllite  (122) 
Aragonite  (56) 
Asbestus  (115) 
Augite  (111) 
Calcite  (50) 


CALCIUM 

Carnotite  (83) 
Chabazite  (128) 
Colemanite  (33) 
Dolomite  (51) 
Epidote  (92) 
Fluorite  (29) 
Grossularite  (88) 
Gypsum  (67) 
Hornblende  (116) 


Laumontite  (126) 
Phillipsite  (123) 
Scheelite  (68) 
Scolecite  (127) 
Stilbite  (125) 
Titanite  (131) 
Tremolite  (113) 
Uvarowite  (88) 
Vesuvianite  (109) 


Carbonates  (50-61) 


Apatite  (72) 
Atacamite  (60) 
Cerargyrite  (26) 


CARBON 
Diamond  (1) 

CHLORINE 

Halite  (27) 
Mimetite  (74) 
Pyromorphite  (73) 


Graphite  (2) 


Sylvite  (28) 
Vanadinite  (75) 


Chromite  (48) 


CHROMIUM 

Crocoite  (71) 


Uvarowite  (88) 


Cobaltite  (20) 
Columbite  (79) 


Atacamite  (69) 
Azurite  (61) 
Bornite  (18) 
Chalcocite  (11) 
Chalcopyrite  (17) 


Apatite  (72) 
Fluorite  (29) 

Gold  (6) 


COBALT 

Erythrite  (77) 

COLUMBIUM 
COPPER 

Chrysocolla  (121) 
Copper  (4) 
Covellite  (12) 
Cuprite  (35) 

FLUORINE 

Lepidolite  (98) 
Topaz  (91) 

GOLD 


Smaltite  (21) 


Samarskite  (81) 


Cyprine  (109) 
Malachite  (60) 
Tetrahedrite  (25) 
Turquoise  (78) 


Vesuvianite  (109) 


MINERALS  ACCORDING  TO  CONSTITUENTS      183 


Actinolite  (114) 
Almandite  (88) 
Andradite  (88) 
Arsenopyrite  (22) 
Augite  (111) 
Biotite  (95) 
Boraite  (18) 
Bronzite  (110) 
Chalcopyrite  (17) 


Anglesite  (65) 
Cerussite  (59) 
Crocoite  (71) 


Lepidolite  (98) 


Actinolite  (114) 
Asbestus  (115) 
Augite  (111) 
Biotite  (95) 
Brittle  micas  (99) 
Bronzite  (110) 
Brucite  (43) 
Chlorites  (100) 


Columbite  (79) 
Franklinite  (49) 
Psilomelane  (173) 
Pyrolusite  (41) 

Cinnabar  (13) 
Molybdenite  (8) 
Niccolite  (19) 
Nitrates  (30-31) 


IRON 

Chromite  (48) 
Columbite  (79) 
Fayalite  (85) 
Franklinite  (49) 
Garnet  (88) 
Goethite  (45) 
Hematite  (38) 
Ilmenite  (132) 
Limonite  (45) 

LEAD 

Galena  (9) 
Mimetite  (74) 
Pyromorphite  (73) 

LITHIUM 

MAGNESIUM 

Chrysotile  (104) 
Dolomite  (51) 
Enstatite  (110) 
Glaucophane  (117) 
Hornblende  (116) 
Hypersthene  (110) 
Magnesite  (52) 

MANGANESE 

Rhodochrosite  (55) 
Rhodonite  (MnSiO3) 
Spessartite  (88) 

MERCURY 
MOLYBDENUM 

NICKEL 
NITROGEN 


Magnetite  (47) 
Marcasite  (15) 
Olivine  (85) 
Pyrite  (14) 
Pyrrhotite  (16) 
Siderite  (53) 
Staurolite  (93) 
Tantalite  (80) 
Wolframite  (69) 


Vanadinite  (75) 
Wulfenite  (70) 


Spodumene  (112) 


Olivine  (85) 
Phlogopite  (95) 
Pyrope  (88) 
Serpentine  (104) 
Spinel  (46) 
Steatite  (105) 
Tremolite  (113) 


Tantalite  (80) 
Troostite  (87) 
Wolframite  (69) 


Wulfenite  (70) 


184 


MINERALS  AND  EOCKS 


Apatite  (72) 
Pyromorphite  (73) 


Alunite  (66) 
Apophyllite  (122) 
Biotite  (95) 
Carnotite  (83) 
Harmotome  (124) 


Opal  (42) 


Argentite 
Cerargyrite  (26) 


PHOSPHORUS 


POTASSIUM 

Lepidolite  (98) 
Leucite  (101) 
Microcline  (119) 
Muscovite  (96) 
Niter  (30) 

SILICON 

Quartz  (34) 

SILVER 

Proustite  (23) 
Pyrargyrite  (24) 


Turquoise  (78) 
Wavellite  (76) 


Orthoclase  (118) 
Phillipsite  (123) 
Phlogopite  (95) 
Psilomelane  (173) 
Sylvite  (28) 


Silicates  (85-132) 
Silver  (5) 


SODIUM 


Albite  (120) 
Analcite  (130) 
Borax  (32) 
Chabazite  (128) 


Glaucophane  (117) 
Halite  (27) 
Natrolite  (129) 
Nephelite  (94) 


Soda-niter  (31) 
Sphene  (131) 
Stilbite  (125) 


Celestiie  (64) 

Arsenopyrite  (22) 
Cobaltite  (20) 
Marcasite  (15) 
Pyrite  (14) 

Tantalite  (80) 
Cassiterite  (40) 

Brookite  (39) 
Ilmenite  (132) 

Scheelite  (68) 


STRONTIUM 


SULPHUR 


Strontianite  (57) 


Pyrrhotite  (16)  Sulphates  (62-67) 

Sulph-antimonites  (23-25)   Sulphides  (7-18) 
Sulph-arsenites  (23-25)        Sulphur  (3; 

TANTALUM 

TIN 
TITANIUM 

Octahedrite  (39)  Titanite  (131) 

Rutile  (39) 

TUNGSTEN 

Wolframite  (69) 


MINERALS  ACCORDING  TO  CONSTITUENTS      185 


URANIUM 

Carnotite  (83)  Uraninite  (84) 

VANADIUM 

Carnotite  (83)  Vanadinite  (75) 

ZINC 

Calamine  (107)  Sphalerite  (10)  Willemite  (86) 

Franklinite  (49)  Troostite  (87)  Zincite  (36) 

Smithsonite  (54) 

ZIRCONIUM 

Zircon  (89) 


YIELDING  WATER  IN  CLOSED  TUBE 

Alunite  (68)  Chrysotile  (104)  Phlogopite  (95) 

Apophyllite  (122)  Colemanite  (33)  Psilomelane 

Atacamite  (60)  Epidote  (92)  Serpentine  (104) 

Azurite  (61)  Erythrite  (77)  Staurolite  (93) 

Bauxite  (44)  Goethite  (45)  Steatite  (105) 

Biotite  (95)  Gypsum  (67)  Tourmaline  (108) 

Borax  (32)  Kaolin  (106)  Topaz  (91) 

Brittle  micas  (99)  Lepidolite  (98)  Turquoise  (78) 

Brucite  (43)  Limonite  (45)  Vesuvianite  (109) 

Calamine  (107)  Malachite  (60)  Wavellite  (76) 

Chlorites  (100)  Muscovite  (96)  Zeolites  (123-130) 

Chrysocolla  (121)  Opal  (42) 


COLLECTIONS 

Suites  of  specimens  to  illustrate  the  minerals  described  in  this  volume  may  be 
obtained  from  Ward's  Natural  Science  Establishment,  Rochester,  N.  Y. 

Collection  No.  1 :   128  specimens,  including  all  but  four  of  the  minerals 

described,  each  in  tray,  1J4  XIJ^  in.,  in  two  pine  boxes $7.50 

Collection  No.  2:   132  specimens,  averaging  1^  X21A  in.,  in  trays 25.00 

Collection  No.  3:   132  specimens,  averaging  3X4  in.,  in  trays 60.00 

Collection  No.  4:  180  specimens,  all  minerals  described  and  varieties, 

averaging  11A  X^Vz  in.,  in  trays 35.00 

Collection  No.  5:  Same,  averaging  3  X4  in.,  in  trays 100.00 


II 

ROCKS 


SYNOPSIS   OF  A   CLASSIFICATION   OF   ROCKS 

A  rock  is  a  structural  unit  of  the  earth's  crust. 

It  may  consist  of  a  single  mineral,  a  mixture  of 
minerals,  a  mixture  of  organic  compounds,  or  a  mix- 
ture of  minerals  and  organic  material.  Its  essential  fea- 
ture is  the  fact  that  it  is  an  integral  portion  of  the  crust. 

On  the  other  hand,  a  mineral  is  a  chemical  com- 
pound which  possesses  definite  properties  because  of 
its  chemical  composition.  The  properties  of  a  rock 
depend  only  partly  upon  its  chemical  composition. 
They  are  determined  also  in  part  by  its  method  of 
occurrence  and  its  origin.  Thus,  granite  possesses 
properties  that  are  due  in  part  to  the  fact  that  it  is 
composed  of  quartz,  orthoclase  and,  perhaps,  biotite, 
but  also  to  the  fact  that  it  is  coarse-grained  and  that 
it  occurs  in  large  structureless  masses,  which  are  the 
result  of  its  manner  of  origin.  The  characters  of 
quartz,  however,  are  due  to  the  fact  that  it  is  composed 
of  a  certain  number  of  silicon  and  oxygen  atoms, 
arranged  in  a  certain  definite  manner  in  its  molecules. 

Stone  is  an  engineering  or  architectural  term  and 
has  no  significance  except  as  indicating  a  certain  kind 
of  structural  material. 

Rocks  may  be  classified  from  the  point  of  view 
of  composition,  of  structure,  or  of  genesis. 

A  classification  according  to  genesis  demands  that 
the  origin  of  the  rock  be  known,  which,  of  course, 

189 


190  MINERALS  AND  ROCKS 

in  many  cases  cannot  be  discovered.  A  genetic 
classification  is  the  only  logical  one,  but  it  can  come 
only  after  all  the  facts  concerning  the  things  classi- 
fied are  known. 

Under  the  present  condition  of  knowledge  con- 
cerning rock  masses,  a  genetic  classification  is  impos- 
sible, except  along  very  broad  lines.  For  our  pur- 
pose, rocks  will  be  considered  as  bodies  to  be  grouped 
according  to  features  they  possess  as  materials. 

In  this  meaning,  the  following  classification  is  pro- 
posed: (A)  crystalline  rocks;  (B)  fragmental  rocks. 
The  former  are  composed  of  material  which  originated 
in  its  present  position,  and  which,  therefore,  is  prin- 
cipally crystalline,  e.g.,  granite;  the  second  class 
includes  those  rocks  formed  of  material  a  large  part 
of  which  originated  elsewhere,  e.g.,  sandstone. 

A.     CRYSTALLINE   ROCKS 

Crystalline  rocks  are  composed  of  minerals  which 
crystallized  from  (1)  aqueous  or  (2)  molten  solutions,  or 
of  minerals  and  glass,  or  of  glass  alone,  formed  by  the 
quick  cooling  of  a  magma.  Another  (3)  group  consists 
of  crystalline  particles  which  have  been  formed  by  the 
reactions  of  gases  and  solutions  upon  the  pre-existing 
components  of  certain  rocks,  or  by  the  reactions  of 
these  components  with  one  another. 

1.  Aqueous  solutions  yield  solid  minerals  upon 
evaporation  or  cooling;  and  the  minerals  normally 
separate  at  the  bottom  of  the  solutions  as  sediments. 

Because  thus  separated,  they  usually  occur  in 
layers  or  strata,  and  because  a  mixed  solution  generally 
precipitates  a  single  substance  until  most  of  it  has  been 
removed  from  the  solution,  rocks  of  this  kind  usually 


SYNOPSIS  OF  A  CLASSIFICATION  OF  EOCKS    191 

consist  of  an  aggregate  of  crystalline  particles  of  a 
single  mineral.  The  aggregate  is  coarse-grained  if 
precipitation  is  slow,  and  fine-grained  if  rapid. 

2.  Molten  solutions  solidify  upon  cooling.     Under 
certain  conditions,  a  given  mineral  may  separate  before 
others  (see  Fig.  96);    under  other  conditions,  several 
minerals  may  separate  simultaneously  (see  Fig.  95); 
under  still  other  conditions,  when  the  cooling  is  so 
rapid  that  crystallization  has  not  had  time  to  take 
place,  the  molten  mass  or  magma  may  solidify  as  a 
glass  (see  Fig.  94). 

3.  Rocks  composed  of  minerals  of  any  kind,  or  of 
particles  of  organic  material,  may  be  acted  upon  by 
gases  or  solutions  which  may  attack  the  components 
and  produce  new  materials.     Or  pressure  may  crush 
the  rock,  breaking  its  components  into  tiny  particles, 
which,  under  the  influence  of  the  pressure  and  the  high 
temperature    produced   by   the    crushing,  may   force 
themselves   into   new   compounds,    especially   in   the 
presence  of  moisture  and  gases. 

Thus,  the  crystalline  rocks  may  be  subdivided  into : 
(1)  chemical  sediments;  (2)  igneous  rocks;  (3)  meta- 
morphic  rocks. 

The  structure,  i.e.,  the  arrangement  of  the  con- 
stituents of  each  class,  is  characteristic.  The  com- 
ponents of  the  chemical  sediments  are  arranged  in 
layers,  i.e.,  they  are  stratified,  like  fragmental  sedi- 
mentary rocks  (see  Fig.  102).  Those  of  many  of 
the  metamorphic  rocks  are  flattened  and  arranged  with 
their  longer  axes  approximately  parallel,  or  at  least, 
in  the  same  plane,  i.e.,  the  rocks  are  schistose  (see  Fig. 
100).  The  igneous  rocks  have  no  definite  arrangement 
of  components.  They  are  said  to  be  massive. 


192  MINERALS.  AND  ROCKS 

With  respect  to  structure  crystalline  rocks  are: 

(1)  Stratified;   (2)  massive;   (3)  schistose. 

The    stratified    crystalline    rocks    are    composed 

essentially  of  crystalline  particles  of  a  single  mineral, 

such  as  might  be  thrown  down  from  solution  by  cooling, 


FIG.  93. — Mass  of  Travertine  (i  nat.  size). 

evaporation,  reactions  or  the  life  processes  of  animals 
or  plants.     The  most  important  are: 

(a)  Ice,  H20. 

(6)  Rocksalt,  NaCl  (halite). 

(c)  Chert,  Si02  plus  Aq.  (chalcedony,  opal,  etc). 

1.  Siliceous  sinter,  composed  of  the  tests  of 
minute  animals  and  plants. 

(d)  Gypsum,  CaSO4. 

(e)  Limestone,  CaC03  or  (Ca-Mg)CO3   (calcite  or 

dolomite). 

1.  Oolite,  composed  of  concretionary  grains 
(Fig.  28). 

2.  Stalactite    (Mexican   onyx),    pendants   of 
radiating  fibers. 

3.  Travertine. — Porous,    composed    of    little 
tubes  (Fig.  93). 


SYNOPSIS  OF  A  CLASSIFICATION  OF  ROCKS     193 

(/)  Limonite,  Fe403(OH)6j  or  Hematite,  Fe2O3. 

1.  Bog  iron  ore. — Porous,  composed  of  little 
tubes,  nodules,  etc.,  of  limonite,  and  con- 
taining often  remains  of  plants. 

2.  Ferruginous  oolite,  composed    of  concre- 
tionary grains  of  limonite  or  hematite. 


FIG.  94. — Glassy  Texture.    Obsidian. 

The  massive  rocks  are  the  result  of  the  cooling  of  a 
molten  magma.  According  to  the  conditions  under 
which  the  cooling  occurred,  i.e.,  whether  under  great 
or  slight  pressure,  whether  rapidly  or  slowly,  etc.,  the 
solid  mass  may  be  composed  of  particles  of  the  same 
or  of  different  sizes  and  shapes,  of  materials  in  the 
same  or  different  states,  etc.  The  result  of  these  vari- 
ations is  known  as  texture.  The  important  textures  are: 

Glassy  or  amorphous  (Fig.  94),  when  the  rock  is 
composed  entirely  of  glass.  The  rock  is  commonly 
known  as  an  obsidian  if  the  glass  is  fresh  and  shiny; 
pitchstone  if  decomposed  and  dull,  irrespective  of 
composition. 


194 


MINERALS  AND  ROCKS 


Felsitic  or  aphanitic,  when  the  rock  material  is  not 
glassy,  but  is  so  fine-grained  that  the  individual  com- 
ponents cannot  be  distinguished. 


FIG.  95. — Granular  Texture.     Granite. 

Granitoid  or  granular  (Fig.  95),  when  the  constitu- 
ents are  equidimensional  grains,  without  crystal  form. 


FIG.    96. — Porphyritic    Texture.     Feldspar    phenocryst    in    granular 

groundmass. 

Porphyritic  (Figs.  96  and  97),  when  some  of  the 
components  are  larger  and  more  conspicuous  (pheno- 
crysts)  than  those  of  the  aggregate  (groundmass)  in 
which  they  lie.  The  groundmass  may  be  glassy  or 


SYNOPSIS  OF  A  CLASSIFICATION  OF  ROCKS    195 

granular.  When  the  phenocrysts  are  quartz  the  rock 
is  sometimes  called  quartz-porphyry.  Its  composition 
is  usually  that  of  a  rhyolite  (p.  197). 


FIG.  97. — Amphibole  Phenocrysts  in  Andesite. 

Vesicular  (Fig.  98),  when  the  mass  of  the  rock 
contains  pores  or  cavities  which  were  made  by  escaping 


FIG.  98. — Vesicular  Texture.    Basalt. 


steam  or  other  vapor.    When  the  pores  are  numerous 
and  very  small  the  rock  is  known  as  pumice. 


196  MINEKALS  AND  EOCKS 

Amygdaloidal  (Fig.  99),  when  the  pores  of  a  vesic- 
ular rock  are  filled  with  mineral  matter  of  a  different 
kind  from  that  composing  the  main  mass  of  the  rock. 

Fragmental,  when  the  rock's  components  consist 
largely  of  fragments  of  minerals  or  particles  of  glass. 

Some  massive  rocks  solidified  at  great  depths,  under 
conditions  which  resulted  in  slow,  continuous  cooling, 
giving  rise  to  the  granular,  or  granitoid  texture,  which 
may  be  coarse-grained  or  fine-grained.  These  are 
characterized  as  plutonic,  because  formed  at  great 


FIG.  99. — Amygdaloidal  Texture,    Basalt. 

depths,  or  intrusive,  because  they  cut  other  rocks. 
Another  class  of  igneous  rocks  solidified  near  the  sur- 
face, where  cooling  was  comparatively  rapid  and  under 
low  pressures.  The  resulting  textures  were  glassy, 
felsitic,  porphyritic,  vesicular  or  amygdaloidal.  These 
are  said  to  be  volcanic,  because  the  best  types  are 
among  the  lavas;  or  extrusive  or  effusive,  because 
most  of  them  flowed  out  over  other  rocks.  A  third, 
comparatively  small  class,  comprises  rocks  which  are 
neither  plutonic  nor  volcanic,  but  are  intermediate  in 


SYNOPSIS  OF  A  CLASSIFICATION  OF  ROCKS    197 

character.  They  are  dike  fillings.  They  represent  the 
roots  of  lava  extrusions,  or  tongues  which  extend  up- 
ward from  plu tonic  masses.  Their  texture  is  more 
frequently  porphyritic  than  otherwise. 

The  separation  of  the  massive  rocks  into  types  is 
based  primarily  upon  their  mineral  composition,  or, 
in  the  case  of  other  than  granular  rocks,  partly  upon 
the  nature  of  their  phenocrysts  and  partly  upon  the 
chemical  composition  of  their  groundmasses. 

The  principal  types  of  massive  rocks  are: 

PLUTONIC  COMPOSITION  VOLCANIC 

(a)  Granite       Quartz  and  alk.  felds>calc.  felds  Rhyolite 

(6)  Syenite       Alk.  felds >calc.  felds  Trachyte 

(c)  Monzonite  Alk.  felds  =calc.  felds  Latite 

(d)  Diorite        Alk.  felds  <calc.  felds  and  hornblende  Andesite 

(e)  Gabbro        Alk.  felds<calc.  felds  and  augite  Basalt 

(/)  Peridotite    Horn.,  augite,  oliv.> felds  Limburgite 

When  so  very  fine-grained  that  their  mineral  com- 
ponents cannot  be  determined,  the  light-colored  kinds 
are  usually  known  by  the  non-committal  name  felsite 
(p.  194)  and  dark  kinds  by, the  name  basalt. 

The  crystalline  schists  are  metamorphic  rocks; 
but  not  all  metamorphic  rocks  are  crystalline  schists. 
The  crystalline  schists  are  crystalline  rocks  which 
exhibit  the  schistose  structure,  i.e.,  those  in  which 
the  components  are  elongated  in  a  common  direction 
(Fig.  100).  In  some  cases  the  rocks  are  also  foliated 
—that  is,  their  elongated  components  are  arranged 
in  indefinite  layers  (Fig.  101),  which,  however,  are 
not  sharply  marked  as  in  the  case  of  stratified  rocks. 

The  crystalline  schists  may  originate  from  igneous 
or  from  sedimentary  rocks;  from  crystalline  or  from 
fragmental  ones.  The  processes  by  which  they  were 


198 


MINERALS  AND  EOCKS 


formed  include  mashing,  crushing  and  solution  and 
deposition.     Mashing  results  in  the  flattening  of.  the 


FIG.  100. — Schistose  Structure.     Gneiss. 

original    components   and    crushing   results   in   their 
fracturing    and    the    movement    of    their  fragments 


FIG.  101. — Foliated  Structure.    Gneiss. 

along  planes  inclined  to  the  lines  of  direction  of  the 
greatest  pressure.  Thus,  the  original  particles  are 
deformed  to  flat  lenses,  the  parts  of  which  are  welded 


SYNOPSIS  OF  A  CLASSIFICATION  OF  ROCKS    199 

together  by  the  deposition  of  material  between  them. 
Solution  and  deposition,  without  crushing,  may  also 
result  in  schistosity,  if  the  processes  occur  in  rocks 
which  are  subjected  to  differential  pressure.  Solu- 
tion of  the  original  components  takes  place  where  the 
greatest  pressure  is  exerted  and  deposition  elsewhere. 
Consequently,  the  original  grains  will  become  thinner 
along  the  directions  of  greatest  pressure  and  be 
elongated  in  directions  approximately  perpendicular. 

The  crystalline  schists  may  be  divided  into  the 
three  groups:  Gneisses,  schists  and  marbles. 

GNEISSES. — The  gneisses  are  comparatively  coarse- 
grained schistose  rocks,  which  may  or  may  not  be 
foliated.  Most  of  them  have  a  mineralogical  composi- 
tion corresponding  to  that  of  some  massive  rocks, 
and  some  of  these  have  undoubtedly  been  derived 
from  massive  rocks.  Others,  having  compositions 
different  from  those  of  the  igneous  rocks,  were  prob- 
ably derived  from  fragmental  rocks.  Their  names 
suggest  their  origin. 

(a)  Granite-gneiss,  with  the  composition  of  granite. 

(6)  Syenite-gneiss,  with  the  composition  of  syenite. 

(c)  Diorite-gneiss,  with  the  composition  of  diorite. 

(d)  Gabbro-gneiss,  with  the  composition  of  gabbro. 

(e)  Peridotite-gneiss,  with  the  composition  of  peri- 

dotite. 
(/)  Conglomerate-gneiss,  of    conglomerate   texture, 

usually  with  the  composition  of  granite. 
SCHISTS. — The  schists  are  fine-grained,  schistose 
rocks,  the  compositions  of  which  are  unlike  those  of 
any  igneous  rock.  Some  of  them  may  have  been  de- 
rived from  igneous  rocks;  but  if  so,  their  composi- 
tions have  been  so  changed  by  metamorphism  that 


200  MINERALS  AND  ROCKS 

their  origin  is  extremely  obscure.  Most  of  them 
were  originally  fragmental  rocks.  The  schists  split 
into  thin  slabs  which  break  apart,  leaving  fairly 
smooth  surfaces.  They  are  named  in  accordance 
with  their  prominent  mineral  component. 

(a)  Mica  schist,  composed  of  mica  and  quartz. 

(b)  Hornblende  schist,  composed  of  hornblende  and 

quartz. 

(c)  Talc  schist,  composed  of  talc,  predominately. 

(d)  Chlorite  schist,  composed  mainly  of  chlorite. 

(e)  Slate,  of  many  minerals,  very  fine-grained. 
MARBLES. — Marbles  are  crystalline  rocks  composed 

mainly  of  calcite  or  dolomite.  Originally,  they  were 
fragrnental  limestones,  but  by  solution  and  deposi- 
tion they  have  in  most  instances  lost  their  fragmental 
characters.  Some  marbles  are  distinctly  schistose, 
but  others  are  apparently  massive.  Their  com- 
ponents are  so  easily  dissolved  and  redeposited  under 
changing  conditions  of  pressure  and  temperature 
that  the  schistose  structure,  if  ever  present,  was  in 
many  cases  subsequently  obliterated. 

B.     FRAGMENTAL   ROCKS 

Fragmental  or  clastic  rocks  are  composed  of  frag- 
ments of  minerals,  of  animal  or  vegetable  matter,  of 
other  rocks  or  of  mixture  of  minerals,  rocks  and 
organic  matter.  Their  materials  are  the  waste  of 
bodies  which  formerly  existed  in  some  other  place. 

These  materials  have  been  brought  together  mainly 
by  some  transporting  agency,  such  as  water,  ice 
in  the  form  of  glaciers,  or  the  air. 

A  small  portion  of  waste  may  remain  on  the  sur- 


SYNOPSIS  OF  A  CLASSIFICATION  OF  ROCKS    201 

face  where  it  was  formed,  or  may  be  transported  short 
distances  by  the  aid  of  gravity,  forming  terrestrial 
deposits  as  distinguished  from  sedimentary  deposits. 
Other  waste  material  may  be  transported  from  one 
portion  of  the  surface  to  another  by  the  wind.  This  is 
assorted  by  the  wind  during  its  transit  and  is  finally 
deposited  in  layers.  The  deposits  thus  formed  are 
terrestrial  in  the  sense  that  they  are  laid  down  on 
the  land,  but  are  sedimentary,  since  they  are  precipi- 


Fio.   102.— Stratified  Sandstone. 

tated  from  the  air.  They  are  known  as  sub-aerial 
deposits. 

Material  dropped  from  water  or  the  air  is  sorted 
and  deposited  in  layers.  That  left  by  glacial  ice 
may  be  unsorted  and  indiscriminately  heaped.  The 
former  is  stratified  (Fig.  102).  Its  origin  is  sedimentary. 
Deposits  left  by  the  ice  are  principally  scattered 
bowlders  and  masses  of  clay  and  bowlders,  known  as 
till,  which,  when  consolidated,  is  sometimes  difficult 
to  distinguish  from  water-deposited  sediments. 

The  waste   that   accumulates  in   the   fragmental 


202  MINERALS  AND  ROCKS 

sediments  may  result  from  the  action  of  (1)  water  in 
the  form  of  frost,  rain,  rivers,  lakes  and  seas,  or  from 
that  of  (2)  volcanoes  during  explosive  eruptions. 
To  these  may  be  added  as  a  third  (3)  class  the  terres- 
trial deposits.  The  material  of  fragmental  rocks  may 
be  aqueo-clastic  or  pyro-clastic. 

Aqueo-clastic  Rocks. — The  aqueo-clastic  rocks  con- 
sist of  deposits  of  the  hard  parts  of  animals  and 
plants  that  lived  in  water  and  of  waste  produced  by 
the  breaking  down  of  rocks  by  various  agencies. 
The  remains  of  land  animals  and  plants  may  be 
washed  into  water  and  deposited  with  other  materials. 
Consolidation  ensues  as  the  result  of  pressure  and  of 
processes  of  cementation.  Rocks  of  this  class  may  be 
separated  into  those  composed  of  material  of  (1) 
inorganic  origin,  and  those  composed  of  (2)  organic 
material.  Most  rocks  of  the  latter  kind  contain  also 
much  inorganic  material. 

Inorganic  Aqueo-clastic  Rocks. —  Inorganic  aqueo- 
clastic  rocks  are  best  classified  on  the  basis  of 
texture,  since  they  are  all  made  of  the  waste  of 
pre-existing  rocks,  and,  therefore,  are  composed  of 
similar  material.  Beginning  with  the  finest  deposits 
we  may  distinguish: 

(a)  Silt,  composed  of  mud,  or  the  finest  portions 
of  worn-down  rocks. 

(6)  Shale ,  a  consolidated  silt  with  the  addition  of 
a  little  cementing  material. 

(c)  Sand,  fragments  of  minerals,  mainly  quartz. 

(d)  Sandstone,  a  sand    cemented    by  the  infiltra- 

tion of  various  substances. 
(1)  Arkose,  in  which  there  are  many  feldspar 
grains,  in  addition  to  quartz. 


SYNOPSIS  OF  A  CLASSIFICATION  OF  EOCKS    203 

(2)  Graywacke,  in  which  are  many  grains  of 

minerals     other     than    feldspar    and 
quartz.     Color  gray  or  greenish. 

(3)  Calcareous  sandstone,  in  which  the  cement 

is  calcite  or  dolomite. 

(4)  Argillaceous    sandstone,    in    which    the 

cement  is  mainly  clay. 

(5)  Ferruginous    sandstone,    in    which    the 

cement  is  limonite  or  some  other  iron 
compound. 

(6)  Quartzite,  in  which  the  cement  is  quartz. 


FIG.  103. — Conglomerate  Pebbles  of  Different  Kinds  in  Sand  Cement. 

(e)  Shingle,  pebbles  and   small  rounded  pieces  of 

rock. 

(/)    Conglomerate,     shingle     cemented     by     finer- 
grained  material  (Fig.  103). 

(g)  Breccia,  composed   of   sharp-edged  fragments 
of  rocks  and  minerals  (Fig.  104). 

Grit,  in  which  the  fragments  are  quartz, 
uniformly  small. 


204  MINERALS  AND  ROCKS 

Organic  Aqueo-clastic  Rocks. — The  organic  aqueo- 
clastic  rocks  are  separable  according  to  composition 
as  follows : 

(A)  CALCAREOUS,  composed  of  carbonates, 
(a)  Limestone,  mainly  CaCOs. 

Shell  limestone,  fragments  of  shells. 
Coral  limestone,  fragments  of  corals. 
Chalk,  fragments  of  tests  of  infusoria. 
Marl,    chalky     material   mixed    with 

clay,  fragments  of  shells,  etc. 
(6)  Dolomite,  mainly  (Mg,Ca)CO3. 


FIG.  104. — Breccia.     Chert  Fragments  in  Sandy  Matrix. 

(B)  CARBONACEOUS,  composed  of  carbon,  hydro- 

carbons, etc. 
(a)    Coal,  altered  plant  remains. 

(C)  PHOSPHATIC,  composed  mainly  of 

Ca4(CaCl)(P04)3. 

(a)  Bone-breccia,  fragments  of  bones. 
(6)  Glauconite,  small  mollusk  shells,  filled  with 

green    phosphatic   clay,  mud   and   glau- 

conite. 

(D)  SILICEOUS,  composed  mainly  of  Si 


SYNOPSIS  OF  A  CLASSIFICATION  .OF  ROCKS    205 

(a)  Infusorial  earth,  tests  of  microscopic  ani- 
mals and  plants. 
(6)  Flint,    compact     chalcedony,   quartz    and 

opal,  in  nodules. 
(E)  FERRUGINOUS,   composed  mainly  of  limonite 

or  hematite, 
(a)  Fossiliferous  iron  ore,  fragments  of  shells 

and  other  parts  of  organisms. 
Pyro-clastic  Rocks. — The  pyro-clastic  rocks  are 
composed  of  material  that  is  blown  from  volcanoes 
and  which  falls  near  the  crater  or  is  wafted  by  the 
wind  to  distant  points.  That  which  falls  into  water 
becomes  stratified.  That  which  falls  on  land  is 
rudely  sorted  but  is  not  distinctly  stratified.  The 
coarsest  material  accumulates  near  the  volcano,  and 
the  finest  at  the  greatest  distance  from  the  center  of 
eruption. 

The  pyro-clastic  deposits  may  be  classified  accord- 
ing to  coarseness  into: 

(a)   Volcanic  breccia,  or  agglomerate. 
(6)    Tuff. 

(c)  Lapilli. 

(d)  Volcanic  sand. 

Terrestrial  Deposits. — The  terrestrial  deposits  are 
placed  here  merely  for  convenience.  They  consist 
of  fragmental  materials  which  are  left  where  formed, 
or  which  have  been  transported  from  one  portion  of 
the  dry  land  surface  to  another.  Their  original 
material  may  have  been  of  aqueo-clastic  or  of  pyro- 
clastic  origin,  or  it  may  have  been  produced  by  the 
disintegration  of  rocks  through  the  chemical  action 
of  +he  atmosphere.  Since  the  deposits  are  formed 
at  the  base  of  the  atmosphere,  they  are  sub-aerial. 


206  MINEKALS  AND  EOCKS 

Only  three  rocks  are  of  sufficient  importance  to  need 
mention  here: 

(a)  Geest,  the  mantle  of  rock  waste  produced  by 
decay  of  pre-existing  rocks. 

Soil,  rock  debris  mixed  with  organic  matter. 
(6)   Loess,    very   fine    clay-like    compacted   dust, 

probably  wind-blown, 
(c)   Sandstone,  consolidated  wind-blown  sand. 

OTHER   ROCKS 

There  are  other  rocks  essentially  different  from  all 
of  those  mentioned  above;  such,  for  instance,  as  the 
dike  rocks  referred  to  on  a  previous  page,  those  pro- 
duced by  the  chemical  decomposition  of  other  rocks, 
e.g.,  clay  (p.  102)  and  serpentine  (p.  100),  and  those 
produced  by  metamorphic  action  around  the  borders 
of  great  igneous  intrusions.  They  are  not  included 
in  this  classification,  however,  because  they  are  of  local, 
rather  than  of  widespread,  occurrence. 


II 


KEY   TO   THE   DETERMINATION   OF   ROCKS 
(EXCEPT  COAL) 

FOR  the  accurate  determination  of  rocks,  their 
field  relations  must  be  studied,  and,  in  many  cases, 
their  sections  must  be  examined  under  the  microscope. 
The  recognition  of  the  true  nature  of  hand  specimens 
is  often  extremely  difficult.  Frequently,  they  can  be 
determined  only  approximately. 

The  following  key  is  arranged  to  guide  the  users 
to  the  discussions  of  the  rock  types  referred  to  in  the 
text.  It  takes  account  only  of  the  most  important 
rocks  and  only  of  those  types  which  are  developed 
with  characteristic  features.  A  key  for  the  determina- 
tion of  all  rock  types  would  be  too  complicated 
for  use  by  anyone  but  a  specialist  in  lithology,  and 
would  demand  the  aid  of  a  microscope.  Rocks  with- 
out well-defined  features,  however,  cannot  be  deter- 
mined by  any  "  key."  They  must  be  studied  in  the 
field  and  under  the  microscope. 
I.  Very  Coarse-grained. 

A.  FRAGMENTAL.  Consists  of  fragments  of 
minerals,  rocks  or  organisms,  in  a  fine- 
grained matrix. 

1.  Fragments    of     rocks    and     minerals, 
rounded  and  pebble-like. — Conglom- 
erate, and  Grit  (p.  203). 
207 


208  MINERALS  AND  ROCKS 

2.  Fragments     sharp-edged.     Breccia    (p. 

203). 

(a)  Fragments  composed  of  igneous 
material.  Cement  is  lava  or 
tuff. — Agglomerate  (p.  205). 

3.  Fragments  consist  of   pieces  of   shells, 

coral  or  other  calcareous  portions  of 
organisms. — Limestone  (p.  204). 

4.  Fragments  consist  of  bones,  teeth,  etc. 

—Bone  breccia  (p.  204). 
B.  CRYSTALLINE.     Contains  no  fragments. 

Not  composed  of  transported  material.— 
Pegmatite  (p.  113). 

Pegmatites  are  named  in  accord  with  their 
mineral  composition   (see  p.  197),    thus: 
granite-pegmatite,  gabbro-pegmatite,  etc. 
II.  Medium  to  fine-grained. — Components  small,  but 

distinctly  visible  to  unaided  eye. 
A.  FRAGMENTAL.     Composed   of   little  spheres, 
sand   grains,   volcanic    ash,  particles    of 
organisms,    or    other   materials.      Often 
stratified. 

1.  Composed  of  limonite  or  hematite. 

(a)  Cellular  limonite. — Bog  iron  ore 

(p.  193). 
(6)   Grains    round,  like    constituents 

of       fish  -  roe.  —  Ferruginous 

oolite  (p.  193). 
(c)   Fragments  of  shells,  corals,  etc.— 

Fossiliferous  iron  ore  (p.  205). 

2.  Composed  of  fragments  of  shells,  or  of 

other  calcareous  materials, 
(a)  Effervesces  in  cold  HC1. 


KEY  TO  THE  DETERMINATION  OF  ROCKS      209 

(1)  Composed  of  fragments  of 

organisms.  —  Limestone 
(p.  204). 

(2)  Composed  of  round  grains. 

-Oolite  (p.  192). 

(3)  Finely  granular. — Chalk  (p. 

204),  or  Marl  (p.  204). 
(b)  Does  not  effervesce  in  cold  HC1 
except  when  in  finest  powder. 
— Dolomitic  limestone  (p.  204). 
3.  Composed  principally  of  sand  grains. — 
Sandstone  (p.  202). 
(a)  Sand  nearly  all  quartz. 

(1)  Cement  is  quartz. — Quartz- 

ite  (p.  203). 

(2)  Cement  is  calcite  or  dolo- 

.  mite. — Calcareous  sand- 
stone (p.  203). 

(3)  Cement  is    clayey. — Argil- 

laceous    sandstone    (p. 
203). 

(4)  Cement  is  limonite  or  other 

iron  compound. — -Ferru- 
ginous sandstone  (p. 
203). 

(6)  Many  of  the  sand  grains  are  feld- 
spar.— Arkose  (p.  202). 

(c)  Sand  very  impure :  contains  shreds 

of  hornblende,  augite,  chlorite, 
etc.  Rock  gray  or  dark  green- 
ish-gray.—Graywacke  (p.  203). 

(d)  Sand    much    mixed    with    clay. 

Stratified.       Chips    easily    to 


210  MINERALS  AND  ROCKS 

flakes. — Arenaceous,  or  sandy, 
shale  (p.  202). 

4.  Composed  of  particles   of   lava,  ashes, 

cinders,  etc.— Tuff  (p.  205). 

5.  Composed  of  fine  powder  that  scratches 

glass. — Siliceous  sinter  and  infusorial 
earth  (pp.  192,  205). 

6.  Composed   of    fine  dust,   often    mixed 

with  clay. — Loess  (p.  206). 
B.  CRYSTALLINE.  Components  formed  in  place. 

Not  transported. 
1.  Composed  of  a  single  mineral. 

(a)  Soluble  in  water. 

(1)  Salty     taste.  — Rock     Salt 
'(p.  192). 

(b)  Not  soluble  in  water. 

(1)  Soluble  in  cold  or  hot  HC1  with 

effervescence. —  Limestone 
(pp.  192,  204). 

(a)  Fibrous,  radiate.— Stalac- 
tite (p.  192). 

jb)  Banded.    Translucent.— 
Mexican  onyx  (p.  192) . 

(c)  Not  banded.      Granular. 

-Marble  (p.  200). 

(d)  Porous,   tubular. — Trav- 

ertine (p.  192).      . 

(2)  Soluble  in  hot  HC1  without 

effervescence, 
(a)  Soft.   Gives  sulphur  test 

on  charcoal.    Gypsum 

(p.  192). 
(6)  Red  or   yellow,   ferrugi- 


KEY  TO  THE  DETERMINATION  OF  ROCKS       211 

nous. — Bog    iron    ore 
(p.  193). 

(3)  Insoluble  in  acids.  Soft.  Rock 

usually    gray. — Soapstone 
(p.  101). 

(4)  Insoluble   in  acids.     Powder 

scratches  glass. — Siliceous 
sinter  (p.  192). 

2.  Composed  of  several  distinct  minerals. 
(A)  Massive.       Components      equidi- 

mensional. 

(1)  Granular.      Components    of 
approximately  equal  sizes. 
(a)  Containing  quartz. 

1.  Containing  much 
orthoclase. — 
Granite  (p.  197). 
(6)  Containing  no  quartz,  or 
only  a  small 
quantity,  but 
some  orthoclase. 

1.  Containing      ortho- 

clase, but  very 
little,  if  any,  pla- 
gioclase.  —  Syen- 
ite (p.  197). 

2.  Containing      ortho- 

clase and  plagio- 
clase. — Monzon- 
ite  (p.  197). 
(c)   Containing    no    quartz 

and  no  orthoclase. 
1.  Containing    plagio- 


212  MINERALS  AND  ROCKS 


clase  and  horn- 
blende. Rock 
light  or  dark 
g  r  a  y. —  Diorite 
(p.  197). 

2.  Containing  plagio- 
clase  and  augite. 
Rock  darker  and 
heavier  than 
d  i  o  r  i  t  e.— Gab- 
bro  (p.  197). 

(d)  Containing  no  feldspar. 
1.  Composed  of  horn- 
blende, augite,  or 
olivine,  or  of  mix- 
tures of  these. — 
Peridotite  (p. 
197). 

(2)  Porphyritic. — Some  constitu- 
ents larger  than  others  and 
usually  with  crystal  out- 
lines. Often  amygdaloi- 
dal. 
(a)  Containing  quartz  in 

phenocrysts. 
1.  Matrix    feldspathic. 
—  Rhyolite      (p. 
197). 
(6)  Containing  no  quartz  in 

phenocrysts. 
1.  Phenocrysts  mainly 
o  f       orthoclase, 
rarely  of  plagio- 


KEY  TO  THE  DETERMINATION  OF  ROCKS       213 

clase. — Trachyte 
(p.  197). 

2.  Phenocrysts  of    or- 
thoclase  and  pla- 
* '    gio clase. — Latite 
(p.  197). 

(c)  No  phenocrysts  of  ortho- 

clase. 

1.  Phenocrysts  of  pla- 

gioclase  and 
hornblende.— 
Andesite(p.l97). 

2.  Phenocrysts  of  pla- 

gioclase  and  au- 
gite. — Basalt  (p. 
197). 

(d)  No  feldspar  phenocrysts. 

1.  Phenocrysts  of  horn- 
blende, augite,  or 
olivine.  —  Basalt 
or  Limburgite  (p. 

197). 

(B)  Schistose  or  foliated.  Constitu- 
ents elongated  in  parallel  direc- 
tions. Rock  often  banded  in  same 
direction.  Splits  more  easily  par- 
allel to  schistosity  than  across 
it. 

(1)  Containing  feldspar. — Gneiss- 
es (p .  1  99) .  The  gneisses  are 
named  in  accordance  with 
their  mineral  composition, 
as  in  the  case  of  massive 


214  MINERALS  AND  ROCKS 


rocks,  thus:  granite-gneiss, 
gabbro-gneiss,  etc. 
(2)  Containing    no    feldspar,    or 
very  little —Schists  (p.  199). 
(a)  Abundant  mica,  usually 
also     quartz.       Mica 
flakes  can  be  pried  off 
by  knife  blade. — Mica 
schist  (p.  200). 
Light  colored. — Musco- 
vite schist  (p.  200). 
Dark  colored. — Biotite 

schist  (p.  200). 
(6)  Abundant  hornblende, 
usually  also  quartz. 
Hornblende  fragments 
can  be  pried  off  by 
knife  blade.  Rock 
usually  black  and  glis- 
tening. —  Hornblende 
schist  (p.  200). 
(c)  Abundant  talc,  usually 
also  quartz.  Soft, 
greasy  feeL  Rock 
white,  gray,  light 
green.  —  Talc  schist 
(p.  200). 

(d)  Abundant  chlorite,  usu- 
ally also  quartz.  Soft, 
lustrous.  Rock  green, 
dark  green  to  almost 
black.  —  Chlorite 
schist(p.  200). 


KEY  TO  THE  DETERMINATION  OF  ROCKS      215 

(e)  Almost  exclusively 
quartz,  with  very  little 
mica,  or  other  flaky 
component.  —  Quartz 
schist  (p.  200). 

3.  Composed  of  several  minerals,  but  so 
fine-grained    that    the    individual 
components  cannot  be  identified, 
(a)  Light-colored.— Felsite  (p.  197). 
(6)  Dark-colored.— Basalt  (p.  197). 
HI.  Dense. — Individual  grains  not  visible  to  un- 
aided eye. 
A.  Glassy,  with  or  without  pores. , 

1.  Full  of  cavities  and  pores. 

(a)  Cavities  minute,  numerous  and  co- 
alescing. Structure  frothy. — Pum- 
ice (p.  195). 

(6)  Cavities  larger,  few  and  separate  and 
«  partly  or  entirely  filled  with  min- 

eral matter.— Amygdaloid  (p.  196). 
N.B. — This  is  a  structure  name. 
The  character  of  the  rock  exhibit- 
ing the  structure  should  be  deter- 
mined. 

2.  No  pores,  or  only  an  occasional  one. 

(a)  Rock  has  brilliant  luster. — Obsidian 

(p.  193). 

(b)  Rock  has  dull  luster. —  Pitchstone 

(p.  193). 

(a)i  and  (6)1.  Containing  little  quartz 
grains.  — Quartz-por- 
phyry (p.  195). 


216  MINERALS  AND  BOOKS 

(a)  2  and  (6)2.  Containing  little  feld- 
spar grains.  -  -  Tra- 
chyte or  Andesite  (p. 
197). 

(a)  3  and  (6)3.  Containing  little  horn- 
blende, augite,  or 
olivine  grains.  —  Ba- 
salt or  Limburgite  (p. 
197). 

B.  Lithoidal  or  Stony.     Dull.     Extremely  fine 
granular. 

1.  Very  hard.     Scratches  steel. 

(a)  Black,  gray,  or  white.  Smooth  frac- 
ture. Nodules  or  thin  layers 
in  chalk  or  limestone. — Flint  (p. 
205). 

(6)  Dark  gray,  yellow.  Porous.  Rough 
fracture.— Chert  (p.  192). 

(c)  White  or  light-colored.  Granular 
fracture. — Quartzite  (p.  203). 

2.  Hard.     Is  scratched  by  steel,  but  not  by 

finger-nail. 

(a)  Effervesces  .when  powder  is  moist- 
ened with  HC1. 

(1)  Small  fragments  dissolve  com- 

pletely or  nearly  completely 
when  treated  with  cold  acid. — 
Limestone  (pp.  192,  204). 

(2)  Small   fragments   dissolve   very 

slowly  in  cold  HC1,  but  rapidly 
in  hot  acid — Dolomite  (pp. 
192,  204). 

(3)  Powder    partly    dissolved,    but 


KEY  TO  THE  DETERMINATION  OF  ROCKS   217 

leaves  clayey  residue  when 
treated  with  acid. — Calcare- 
ous shale  (p.  202). 

(&)  Does  not  effervesce  with  hot  HC1, 
even  in  powder. 

(1)  Stratified.     Usually  breaks  into 

chips  parallel  to  bedding, 
(a)  Clayey  odor  when  breathed 
on. —Shale  (p.  202). 
(a)i  Gives  Phosphorus  re- 
act i  o  n. — P  h  o  s  - 
p  hat  e  rock  (p. 
204). 

(2)  Schistose.     Splits  with  smooth 

fracture  into  plates,   usually 
across    bedding.      Frequently 
rings  when  struck  by  steel, 
(a)  Rock  generally  homogene- 
ous.—Slate  (p.  200). 

(3)  Massive. 

(a)  Black.— Basalt,  or Limburg- 
ite  (p.  197). 

(.6)  White,  light  gray,  red,  pur- 
ple, rarely  green. — Fel- 
site  (p.  197). 

(c)  Pale  to  dark  green,  often 
crossed  by  veins  of  white 
or  light  green  talc  or  cal- 
cite.  Translucent.  Waxy 
luster.  Soluble  in  hot 
HC1  leaving  residue  of 
gelatinous  silica.  —  Ser- 
pentine (pp.  100,  206). 


218  MINERALS  AND  ROCKS 

3.  Very  soft.     Scratched  by  finger-nail. 

(a)  When  rubbed  between  the  fingers, 

feels  smooth  and  greasy. 
(1)  Has    clayey   odor.  —  Clay   (pp. 

102,  206). 

(6)  When    rubbed    between    fingers    it 
crumbles  to  powder. 

(1)  Effervesces  briskly  with  HC1. 

(a)  Porous,  tubular. — Calc  sin- 
ter or  travertine  (p.  192). 

(6)  Finely-granular. — Chalk  (p. 
204)  or  Marl  (p.  204). 

(c)  Neither  (a)  nor  (6).  Com- 
pacted dust. — Loess  (p. 
206). 

(2)  Does  not  effervesce  briskly  with 

HC1. 

(a)  Powder  scratches  glass.— 
Siliceous  sinter  and  in- 
fusorial earth  (pp.  192, 
205). 

(6)  Gives  sulphur  reaction. — 
Gypsum  (p.  192). 

(c)  Neither  (a)  nor  (b).  Com- 
pacted dust. — Loess  (p. 
206). 


INDEX 


Achroite,  104 

Acid    potassium    sulphate,    131, 

147,  148. 

Actinolite,  110,  177,  182,  183 
Adularia,  115 
Agate,  34 
Agglomerate,  205 
Alabaster,  66 
Albite,  116,  181,  184, 
Alkalies,  144-146 
Almandite,  85,  183 
Alum,  64 
Alumina,  147 
Aluminates,  46-49 
Aluminium,  44,  45,  64,  181 
Aluminium,  reactions  of,  147,  151 
Alunite,  64, 177, 179, 181, 184, 185 
Amber  mica,  93,  94 
Amethyst,  34 
Amorphous  rocks,  193 
Amphiboles,  109-112 
Amygdaloidal  rocks,  196 
Analcite,  124,  178,  179,  184 
Andalusite,  87,  177,  179,  181 
Andesine,  116 
Andesite,  195,  197 
Andradite,  85,  182,  183 
Anglesite,  63,  176,  177,  178,  179, 

183 

Anhydrite,  60,  61,  175,  178,  182 
Ankerite,  175,  178,  179 
Anorthite,  116,  181,  182 
Antimony,  12,  13,  172,  181 
reactions  of,  136,  138,  151 


Apatite,  70,  71,  175, 176, 178, 179, 

182, 184 

Aphanitic  rocks,  194 
Apophyllite,   120,  121,   177,  178, 

179,  182,  184,  185 
Apparatus  for  mineral  tests,  129, 

130 

Aquamarine,  100 
Aqueo-clastic  rocks,  202-205 
Aragonite,  56,  57,  176,  177,  178, 

179,  182 
Argentite,  184 
Argillaceous  sandstone,  203 
Arkose,  202 
Arsenates,  70-77 
Arsenic,  24,  181 

reactions  of,  136,  138,  151,  152 
Arsenides,  22-25 
Arsenopyrite,  24,  170,  181,  183, 

184 

Asbestus,  100,  111,  180,  182,  183 
Atacamite,  175,  182,  185 
Augite,  108,  172,  175,  177,  181, 

182,  183 
Azurite,  59,  60,  175,  182,  185 

Balas  ruby,  47 

Barite,  15,  16,  61,  62,  176,  178, 

179,  181 
Barium,  58,  181 

reactions  of,  145,  152 
Barium  salts,  62 
Basalt,  195,  196,  197 
Basaltic  hornblende,  111 


219 


220 


INDEX 


Bauxite,  44,  45, 173,  174, 179, 181, 

185 

Beads,  use  of,  140-142 
Beryl,  99,  177-181 
Beryllium,  181 
Biotite,  93, 172, 175, 176, 183, 184, 

185  '''V^.'i 

Bismuth,  reactions  of,  135, 139, 152 
Black  lead,  9 
Blende,  15,  16 
Bloodstone,  34 
Blowpipe,  128,  131-134 
Blue  beryl,  100 
Blue  litmus  paper,  131 
Bog  ore,  46,  193 
Bone-breccia,  204 
Borates,  31-33 

Borax,  31-33,  131,  181,  184,  185 
Bornite,  10,  21,  22,  170,  182,  183 
Boron,  181 

reactions  of,  143,  152,  153 
Bort,  8 

Brazilian  emerald,  104 
Brazilian  sapphire,  104 
Breccia,  203,  204,  205 
Brittle  micas,  95,  181,  183,  185 
Bromides,  148 

Bromines,  reactions  of,  148,  153 
Bronzite,  106,  107,  177,  183 
Brookite,  40,  171-176,  184 
Brown  clay  ironstone,  46 
Brown  hematite,  45,  46 
Brucite,  43,  176-179,  183,  185 
Bucklandite,  90 
Bunsen  burner,  129 
Bytownite,  116 

Cadmium,  reactions  of,  139,  153, 

154 

Cairngorm,  34 

Calamine,  102,  176,  178,  179,  185 
Calcareous  rocks,  204 
sandstone,  203 


Calcite,  6,  10,  15,  50-52,  106,  175- 

179,  182,  192 
Calcium,  182 

reactions  of,  143,  145,  154 
Californite,  105 
Carbon,  182 

Carbonaceous  rocks,  204 
Carbonado,  8 
Carbonates,  49-60,  182 
reactions  of,  149,  150 
Carnallite,  177 
Carnelian,  34 
Carnotite,  80,  81,  174,  182,  184, 

185 
Cassiterite,    40,    41,    71,    89,    95, 

171-176,  178,  184 
Celestite,  62,  63,  178,  179,  184 
Cerargyrite,  27,  28,  176-177,  179, 

182,  184 
Cerium,  78 
Cerussite,  58,  59,  175,  177,  179, 

183 

Ceylonite,  47 
Chabazite,     123,     124,     176-179, 

182,  184 
Chalcedony,  34 
Chalcocite,  16,  170,  182 
Chalcopyrite,  10,  16,  21,  25,  170, 

182,  183 
Chalk,  51,  204 
Charcoal   in   mineral   tests,    130, 

136-140 
Chert,  192 
Chiastolite,  88 
Chile  saltpeter,  31 
Chlorates,  147 
Chlorides,  27-30 

reactions  of,  148 
Chlorine,  182 

reactions  of,  146,  147,  148,  154 
Chlorite-schist,  200 
Chlorites,  96,  97,  175,  176,  183, 

185 


INDEX 


221 


Chloritoid,  96,  175,  177 
Chromates,  66-70 
Chrome-iron  alloy,  48 
Chromite,  48,  171,  173,  182,  183 
Cfiromium,  48,  182 

reactions  of,  141,  146,  149,  154, 

155 
Chrysocolla,   119,   120,  173,   175, 

176,  178,  182,  185 
Chrysoprase,  34 
Chrysotile,    100,    176,    177,    179, 

183,  185 

Cinnabar,  17,  170,  172-174,  183 
Citrine,  34 
Clay,  101,  102 
ironstone,  39 
Cleavage,  6 
Clinochlor,  96 
Clintonite,  176 
Closed  tube,  use  of,  134,  135 
Coal,  204 
Cobalt,  23,  76,  182 

reactions  of,  138,  141,  155 
nitrate,  131,  147 
Cobaltite,  23,  24,  170,  181,  182, 

184 
Colemanite,  31-33,  179,  181,  182, 

185 

Color,  changes  of,  135 
Coloration  of  flame,  142-146 
Columbates,  77-79 
Columbite,  77,  78,  170,  171,  182, 

183 
Columbium,  182 

reactions  of,  141,  149,  155 
Conglomerate,  199,  203 
Copper,  9,  16,  21,  22,  26,  59,  62, 

82,  120,  170,  182 
reactions  of,  138,  141,  146,  155 
oxide,  131 
Coral,  204 

Corundum,  36-38,  170,  171,  173, 
176-181 


Covellite,  16-18,  170,  182 
Crocidolite,  175 
Crocoite,  69,  70,  174,  182,  183 
Crystalline  rocks',    190-200,   208, 

210 

Crystallization,  3 
Cuprite,  35,  36,  59,  170-174,  182 
Cyanite,  98,  181 
Cyprine,  106,  182 

Decrepitation,  137 

Deflagration,  137 

Density,  5 

Diallage,  108 

Diamond,  7,  8,  175,  176,  180,  182 

Didymium,  141 

Diorite,  197,  199 

Disthene,  98 

Dolomite,  52,  53,   175,  176,  177. 

178,  179,  182,  183,  192,  204 
Dry-bone  ore,  54,  55 

Edenite,  111 

Elements,  7-12 

Emerald,  100 

Emery,  37 

Endlichite,  73 

Enstatite,  106,  176,  177,  178,  180, 

183 

Epidote,  89,  90,  175-178,  182,  185 
Erbium,  78 
Erythrite,  24,  75, 174, 181,182,185 

Fassaite,  108 
Fayalite,  83,  183 
Feldspars,  112-119,  194 
Felsitic  rocks,  194 
Ferberite,  68,  173 
Ferrites,  46-49 
Ferruginous  oolite,  193 
Ferruginous  rocks,  205 
Ferruginous  sandstone,  203 
Fertilizers,  mineral,  61,  66,  71 


222 


INDEX 


Fire  opal,  43 
Flame,  blowpipe,  131 

Bunsen,  129 

Flame  coloration,  142-146 
Flint,  35,  205 
Fluorides,  27-30 

reactions  of,  148 
Fluorine,  29,  182 

reactions  of,  135,  148,  155,  156 
Fluorite,  15,   16,  29,  30,  67,  175, 

176,  177,  178,  179,  182 
Fluorspar,  29,  30 
Forsterite,  83 
Fossil  ore,  39,  205 
Fowlerite,  177 
Fragmental  rocks,   196,  200-206, 

207,  208 
Franklinite,    48,    84,    170,    171, 

183,  185 
Fusibility,  136,  137 

Gabbro,  197,  199 

Galena,  15,  16,  22,  55,  58,  59,  63, 

170,  183 
Garnet,  85,  86,  106,  172,  175-178, 

180,  181,  183 
Geest,  206 
Gem  stones,  7/8,  34,  37,  43,  47,  67, 

76,  77,  84-89,  99-100,  103- 

106,  109,  119 

Glass  in  mineral  tests,  130 
Glassy  rocks,  193,  215 
Glauconite,  175,  176,  204 
Glaucophane,  112,  175,  179,  181, 

183,  184 
Gneiss,  198,  199 
Goethite,  45,  173,  183,  185 
Gold,  11,  12,  182 

reactions  of,  138,  156,  157 
Golden  beryl,  100 
"  Gossan,"  20 
Granite,  194/197,  199 
Granitoid  rocks,  194 


Graphite,  8,  9,  170,  172,  173,  182 
Graywacke,  203 
Grossularite,  85,  182 
Gypsite,  66 

Gypsum,   9,   33,   57,   61,   64-66, 
175-179,  182,  185,  192 

Halite,  28,  29,  66,  175-179,  182, 

184,  192 

Hardness,  Moh's  scale  of,  4 
Harmotome,  122,  176,  178,  179, 

181,  184 

Heat,  sources  of,  129,  130 
Heavy  spar,  61,  62 
Heliotrope,  34 
Hematite,  38,  39,  170,  171,  173, 

174,  183,  193 
Heulandite,  182 
Hessonite,  85 
Hiddenite,  109 
Horn  silver,  27,  28 
Hornblende,   111,   112,    171-173, 

175,  176,  177,  181-183,  200 
Huebnerite,  68,  171,  172,  173,  174, 

175,  176,  178 
Hyacinth,  87 
Hyalite,  43 

Hydrated  silicates,  119-121 
Hydrochloric  acid,  131,  148-150 
Hydrofluoric  acid,  135 
Hydrogen  sulphide,  134 
Hydroxides,  42-46 
Hypersthene,  107,  172,  175,  177, 

183 


Ice,  192 

Iceland  spar,  51 

Ilmenite,  126,  127,  170,  171,  183, 

184 

Indicolite,  104 
Indigo  copper,  17 
Infusorial  earth,  43,  205 
Intrusive  rocks,  196 


INDEX 


223 


Iodides,  147 

Iodine,  reactions  of,  147,  157 
Iron,  21,  38,  41, 48,  54,  59, 102, 183 
reactions  of,  138,  141,  157,  158 
Iron  pyrites,  18 
Iron  sulphides,  18 

Jasper,  35 

Kaolinite,  101,  102,  176,  177,  178, 

181,  185 

Key  to  rocks,  207-218 
to  minerals,  170-180 
Kunzite,  109 
Kyanite,  98,  179,  181 

Labradorite,  116,  175,  177 

Land  plaster,  61,  66 

Lapilli,  205 

Latite,  197 

Laumontite,   123,   176,  177,   178, 

179,  182 
Lead,  9,  13,  14,  25,  58,  59,  62-64, 

72,  82,  102,  183 
reactions  of,  135,  139,  143,  158 
Lepidolite,  95,  105,  177,  179,  182- 

185 

Lepidomelane,  93 
Leucite,  97,  180,  181,  184 
Limburgite,  197 
Lime,  52 
Limestone,   51,   61,   64,   66,   192, 

193,  204 
Limonite.  20,  45,  59, 171, 172, 174, 

183,  185,  193 
Lithium,  183 

reactions  of,  143,  144,  145,  158 
salts,  95 

Lithoidal  rocks,  216-218 
Loess,  206 
Luster,  3,  4 

Magnesia,  53 
Magnesian  limestone,  52 


Magnesite,  52,  53,  175-177,  179, 

183 
Magnesium,  183 

reactions  of,  147,  159 
Magnesium  ribbon,  131,  149 
Magnetic  pyrites,  18 
Magnetite,  47,  48,  71,  170,  183 
Malachite,  59,  60,  175,  182,  185 
Mangan-apatite,  71 
Manganese,  56,  183 

reactions  of,  141,  146,  159,  160 
Marbles,  200 

Marcasite,  18,  19,  170,  183,  184 
Marl,  204 
Massive  rocks,  193-197,  211,  212, 

213,  217 
Melanite,  85 
Mercury,  13,  17,  183 

reactions  of,  135,  136,  160 
Metamorphic  rocks,  197-200 
Mexican  onyx,  51,  192 
Mica,  92-97,  181,  200 
Microcline,    115,    116,    177,    180, 

181,  184 

Microcosmic  salt,  131 
Milky  quartz,  34 

Mimetite,  72,  176,  177,  179,  181, 

182,  183 

Mineral  fertilizers,  61,  66,  71 
Mineral  tests,  apparatus  for,  129, 

130 
Minerals,  composition  of,  2 

key  to,  170-180 

reactions  of,  151-167 
Mispickel,  24 
Moh's  scale  of  hardness,  4 
Molybdates,  66-70 
Molybdenite,  13,  14,  67,  170,  172, 

183 
Molybdenum,  13,  69,  183 

reactions  of,  138,  139,  141,  149, 

160 
Monzonite,  197 


224 


INDEX 


Moonstone,  115 

Muscovite,  94,  95,  176,  177,  179, 
184,  185 

Natrolite,  124,  178,  179,  184 
Nephelite,  91,  177,  178,  179,  181, 

184 

Niccolite,  23,  170,  181,  183 
Nickel,  23,  183 

reactions  of,  138,  141,  160,  161 
Niter,  31,  131,  179,  184 
Nitrates,  31,  183 

reactions  of,  147 
Nitric  acid,  reactions  of,  161 
Nitrites,  reactions  of,  147 
Nitrogen,  183 
Nitrogen  peroxide,  135 
"  Norite,"  20 

Obsidian,  193 

Ocher,  39 

Octahedrite,  40,  175,  176,  184 

Oligoclase,  116,  118 

Olivine,  83,  84,  176,  177,  178,  183 

Onyx,  34 

Oolite,  192 

Oolitic  ore,  39 

Opal,  42,  43,  177,  178,  179,  180, 

184,  185 

Open  tube,  use  of,  135,  136 
Oriental  amethyst,  37 
Oriental  emerald,  37 
Oriental  topaz,  37 
Orthoclase,    113-115,    177,    178, 

180,  181,  184 
Oxides,  33-42 
Oxygen,  reactions  of,  161 

Paragonite,  95,  179 
Pegmatite,  113 
Pentlandite,  20 
Peridot,  84 
of  Ceylon,  104 


Peridotite,  197,  199 

Perthite,  115 

Phenocrysts,  194 

Phillipsite,  122,  178,  179,  182,  184 

Phlogopite,  93,  176-179,  183-185 

Phosphates,  70-77 

Phosphatic  rocks,  204 

Phosphoric    acid,     reactions    of, 

143,  149,  161,  162 
Phosphorite,  71 
Phosphorus,  149,  184 
Physical  properties  of  minerals, 

2-6 

Picotite,  47 
Pigments,  15,  16,  19,  24,  42,  46, 

57,  62,  74 
Pitchblende,  81,  82 
Pitchstone,  193 
Plagioclase,  116-119,  180 
Plasma,  34 

Plaster  of  Paris,  65,  66 
Platinum  in  mineral  tests,  130, 172 
Plumbago,  9 
Plutonic  rocks,  196 
Porphyritic  rocks,  194 
Potash,  97 
Potassium,  29,  64,  145,  184 

reactions  of,  144,  145 
Prochlorite,  96 
Proustite,  25,  26,  170,  174,  181, 

184 

Psilomelane,  173,  181,  183-185 
Pumice,  195 
Pyrargyrite,  25,  26,  170,  174,  181, 

184 

Pyrite,  11, 18-20,  25, 170, 183, 184 
Pyro-clastic  rocks,  205,  206 
Pyrolusite,  41,  42,  170,  183 
Pyromorphite,  71,  72,   174,   175, 

176,  177,  179,  182-184 
Pyrope,  85,  183 
Pyroxenes,  106-109 
Pyrrhotite,  18,  20,  170,  183,  184 


INDEX 


225 


Quartz,  11,  15,  33-35,  106,  175- 

176,  178-180,  184 
Quartz-phorphyry,  195 
Quartzite,  203 

Radium,  79,  80,  81,  82 

Reactions  of  minerals,  151-167 

Reagents,  131 

Reduction,  137 

Rhinestone,  34 

Rhodochrosite,  55,  56;  176,  177, 

178,  179,  183 
Rhodonite,  177,  183 
Rhyolite,  197 
Rock  crystal,  34 
Rock-gypsum,  66 
Rock  salt,  61,  64,  192 
Rocks,    composition    of,    1,    189, 

190 

key  for,  207-218 
Rubellite,  95,  104 
Ruby,  37 
Ruby  spinel,  47 
Rutile,  39,  40,  171-177, 184 

Salt,  28,  29 

of  phosphorus,  131 
Samarskite,  78,  79,  170,  171,  182 
Sanidine,  115 
Sand,  202 
Sandstone,    201,    202,    203,    206, 

209,  210 
Sapphire,  37 
Sardonyx,  35 
Satin  spar,  51,  66 
Scheelite,  66,  67,  176,  178,  179, 

182,  184 
Schistose  rocks,  197-200,  213,  214, 

216,  217 

Scolecite,  123,  179,  182 
Selenite,  66 
Selenium,  reactions  of,  136,  139, 

143,  162 


Serpentine,  100, 101, 175, 176, 177, 

178, 183,  185 
Shale,  202 
Shell,  204 
Shiogle,  203 
Siderite,  54,  171,  172,  173,  174, 

179,  183 

Silica,  reactions  of,  141 
Silicates,  82-106,  184 
Siliceous  rocks,  204 
Siliceous  sinter,  43,  192 
Silicon,  184 

reactions  of,  141,  162,  163 
Silt,  202 
Silver,  10, 11, 15, 16,  25-28,  62, 82, 

172,  184 

reactions  of,  138 
Slate,  200 

Smaltite,  23,  24,  170,  181,  182 
Smithsonite,  54,  55,  176,  177,  178, 

179,  185 

Smoky  quartz,  34 
Soapstone,  101 
Soda-niter,  31,  179,  184 
Sodium,  184 

reactions  of,  143,  144,  145,  148 
Sodium  carbonate,  131 
Sodium  tungstate,  67 
Soil,  206 

Spectroscope,  143 
Specular  ore,  39 
Spessartite,  85,  183 
Sphalerite,  15,  16,  22,  25,  55,  171- 

176,  177,  178,  185 
Sphene,  125,  126,  184 
Spinel,  47,  171,  172,  175-179,  181, 

183 

Spodumene,  109,  181,  183 
Stalactite,  51,  192 
Staurolite,  90,  91,  170,  175,  176, 

181,  183,  185 
Steatite,  101,  183,  185 
Stibnite,  12,  13,  170,  181 


226 


INDEX 


Stilbite,  122,  176,  177,  178,  179, 

182,  184 

Stratified  rocks,  192,  193,  217 
Streak,  3,  170-180 
Stream  tin,  41 

Strontianite,  57, 176, 177, 179, 184 
Strontium,  57,  63,  184 

reactions  of,  145,  163 
Sublimates,  135 
Sublimation,  137 
Sulph-antimonites,  25-27,  184 
Sulph-arsenides,  22-27,  184 
Sulphates,  60-66,  184 
Sulphides,  12-22,  184 

reactions  of,  148 
Sulphur,  9,  174,  177,  184 

reactions  of,  136,  146,  148,  163 
Sulphuric  acid,  9,  131 
Sunstone,  115 
Syenite,  197,  199 
Sylvite,  29,  178, 179,  182, 184 

Talc,  101,  176,  177,  178,  179,  200 
Tantalite,  77,  78,  170,  171,  183, 

184 

Tantalum,  78,  184 
reactions  of,  163 
Tellurium,  reactions  of,  136,  139, 

164 

Tenacity,  5 
Tephroite,  177 

Tetrahedrite,  26,  170,  171,  181 
Thollium,  143 
Thorium,  78 
Tin,  40,  41,  184 

reactions  of,  139,  147 
Titanite,  125,  126,  172,  175,  176, 

177,  178,  182,  184 
Titanium,  125,  184 

reactions  of,  141,  149,  164,  165 
Topaz,  67,  88,  89,  177-182,  185 
Tourmaline,    95,    103-105,    172, 

175-181,  185 


Trachyte,  197 

Travertine,  5l,  192 

Tremolite,     110,    177,    179,    182, 

183 

Tripoli,  43 
Tripolite,  176 

Troostite,  84,  176,  183,  185 
Tuff,  205 
Tungstates,  66-70 
Tungsten,  66-68,  184 

reactions  of,  138,  141,  149,  165 
Turmeric  paper,  131 
Turquoise,  76,  77,  175,  177,  179, 

181,  182,  184,  185 

Uraninite,  81,  82,  170-173,  175, 

185 
Uranium,  80,  81,  82,  185 

reactions  of,  141,  165,  166 
Uranyl  compounds,  80-82 
Uvarowite,  85,  182 

Vanadinite,  73,  74,  174,  176-179, 

182,  183,  185 
Vanadium,  74,  80,  81,  185 

reactions  of,  141,  149,  166,  167 
Vesicular  rocks,  195 
Vesuvianite,   105,   106,   176,   177, 

178,  179,  181,  182,  185 
Vivianite,  175 
Volatilization,  136 
Volcanic  breccia,  205 
Volcanic  rocks,  196,  197 
Volcanic  sand,  205 

Wad,  170,  171,  173,  174 
Wavellite,  74,  75,  175,  176,  177, 

178,  179,  181,  184,  185 
White  lead,  15 
White  pyrites,  18 
Willemite,  84,  177,  178,  180,  185 
Withamite,  90 
Witherite,  57,  5B,  179,  181 


INDEX 


227 


Wolframite,  67,  68,  170,  171,  173, 

174,  183,  184 
Wollastonite,  179 
Wood  tin,  41 
Wulfenite,  68,  174,  176,  177,  178, 

179,  183 

Yellow  ocher,  46 
Yttrium,  78 
Yttrotantalite,  78,  79,  175 


Zeolites,  121-125,  181,  185 
Zinc,  13,  15,  16,  36,  54,  55,  84, 
85,  102,  185 

granulated,  131 

reactions  of,  139,  147,  148,  167 
Zincite,  36,  84,  171,  174,  185 
Zircon,  86,  87,  176,  178,  180,  185 
Zirconia,  87 
Zirconium,  18£ 

reactions  of,  167 


(2) 


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